JP3524434B2 - Grouting material for ground injection - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground pouring grout material suitable for preventing liquefaction of ground by using acidic silica sol composed of acid and water glass, and particularly for a long time during the liquefaction prevention work of the ground. The present invention relates to a ground-grouting material that is injected to achieve large-scale ground improvement.

[0002]

2. Description of the Related Art In recent years, with the development of landfill sites, there has been a demand for an injection material capable of preventing liquefaction of the ground. As an injection material that prevents the liquefaction of the ground, it must be an injection material that solidifies a vast area and suppresses the flow of groundwater.

As such an injection material, generally,
The injection material has a long gelation time so that it spreads over a wide range, and it shows high permeability by reducing the shortening of the gelation time especially in soil. It is preferably close to neutral.

As such a grout material, conventionally, a solution-type water glass grout using ultrafine particle silica or acidic silica sol has been developed.

[0005]

However, the solution type water glass grout using ultrafine particle silica has high viscosity and poor permeability with gelation, and moreover, the gelation time is adjusted, especially for long gels. It is extremely difficult to adjust the activation time.

[0006] Further, the solution type water glass type grout using the acidic silica sol is infiltrated into the ground, the pH value shifts from acidic to neutral due to contact with earth and sand. Since it is remarkably shortened, a wide injection range cannot be obtained as a ground liquefaction prevention grout, which is unsuitable.

Therefore, the inventors of the present invention have found that the gelling time of the injection material is shortened in the ground not only because the pH value of the injection liquid shifts to neutrality but also in the ground. It was judged that metal ions, especially calcium ions, iron ions, aluminum ions, etc., react with silica in the injecting material to form a polyvalent metal salt and accelerate gelation, and formation of these polyvalent metal salts is judged. The inventors have found that the suppression of the gelation time can be suppressed by suppressing it, and have completed the present invention.

The object of the present invention is not only to increase the gelation time per se, but also to reduce the shortening of the gelation time even when the soil is contacted with the soil, and to continuously inject the soil particles for a long time. It is an object of the present invention to provide a ground injection grout material which is effective in preventing the liquefaction of the ground by reducing the decrease in permeation due to the sedimentation of gel between soil particles, and which has improved the above-mentioned drawbacks of the known art.

[0009]

In order to achieve the above object, according to the present invention, one or both of a sequestering agent and a phosphoric acid compound is added as an active ingredient to an acidic silica sol consisting of an acid and water glass. As a result, the pH is adjusted to 2.8 or less, and by adjusting the pH value in the acidic region, not only the gelation time of itself is long, but also the gelation occurs even when it contacts soil in the ground during injection. The feature is that the reduction of time is reduced.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

Conventional acidic silica sols consist of excess acid (usually sulfuric acid) and water glass. PH in acidic range
The gelation time becomes shorter as the ratio increases and the SiO ₂ concentration increases. Therefore, in order to obtain a long gelation time, it is necessary to lower the pH and the SiO ₂ concentration.
However, in general, if the gelation time is extended as described above, the strength is of course deteriorated.

Also, depending on the nature of the injection ground,
Injecting into the ground generally shortens the gelation time in many cases. Since the conventional acidic silica sol exhibits such a phenomenon, there remains a problem in applying it as a ground liquefaction preventing grout.

The present invention solves the above-mentioned problems by including one or both of a sequestering agent and a phosphoric acid compound in an acidic silica sol as an active ingredient so that the pH value is in an acidic region of 2.8 or less. We were able to. Of course, the above-mentioned sequestering agents and phosphoric acid compounds may be used alone or in combination of two or more kinds. Further, another reagent may be added for adjusting the pH. When the pH value is 2.8 to 3.0 or more, the gelation time in homogel and soil is rapidly accelerated and becomes unstable.

Examples of the above-mentioned sequestering agents include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, propylenediaminetetraacetic acid, bis (2-hydroxyphenylacetic acid) ethylenediamine and succinic acid. Examples thereof include salts, aliphatic oxycarboxylic acids and salts thereof, condensed phosphates and the like.

Aliphatic oxycarboxylic acids include tartaric acid, citric acid, gluconic acid, dihydroxyethylglycinic acid and the like, and salts thereof, and condensed phosphates such as pyrophosphoric acid, triphosphoric acid, trimetaphosphoric acid and tetrametaphosphoric acid. Specific examples of the salt of polyphosphoric acid include sodium pyrophosphate, sodium acid pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, sodium hexametaphosphate, sodium acid hexametaphosphate and potassium salts thereof.

The phosphoric acid-based compound is other than the above-mentioned condensed phosphoric acid salt, for example, ordinary phosphoric acid, orthophosphoric acid salt, acidic phosphoric acid salt and the like.

The grout material according to the present invention thus formed has a long gelation time per se, exhibits a relatively low viscosity until immediately before gelation, and has a short gelation time in soil. This means that the sequestering agent acts as a sequestering agent for a trace amount of metal in the soil, and the phosphoric acid-based compound condenses in the soil to exhibit a sequestering action, and significantly suppresses the formation of a metal salt, It is presumed that this is due to the synergistic effect that the increase in pH in the soil becomes slow due to the buffering action of the sequestering agent. Such an effect is remarkable especially in the case of containing citric acid or a salt thereof.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

1. Materials to be used (1) Water glass Water glass of various molar ratios, particularly JIS No. 3 water glass and water glass of even higher molar ratio are preferable. Here, the most commonly used JIS No. 3 water glass having the following composition is used.

Specific gravity (20 ° C.): 1.39, SiO ₂ : 2
9.2%, Na ₂ O: 9.5%, molar ratio: 3.17

(2) Sulfuric acid 75% industrial sulfuric acid

(3) Sequestering agent (a) Ethylenediaminetetraacetic acid C ₁₀ H ₁₆ N ₂ O ₈ (b) Citric acid Industrial chemicals

[Chemical 1] (C) sodium citrate _{C 6 H 5 O 7 Na 3} · 2
H ₂ O (d) condensed phosphate sodium hexametaphosphate (NaPO ₃ ) ₆ sodium acid pyrophosphate Na ₂ H ₂ P ₂ O ₇

[0023] (4) a phosphate-based compound (a) phosphoric acid 75% technical phosphoric acid (b) sodium dihydrogen phosphate NaH ₂ PO ₄ · 2
H ₂ O

(5) Sodium hydrogen carbonate reagent first grade NaHCO ₃

(6) Toyoura sand is used as the fine sand, and sea sand from Chiba Prefecture is used as the silty sand.

2. Measurement method (1) Unconfined compressive strength of sand gel The sand gel of Toyoura sand was subjected to polyvinylidene chloride closed curing (20 ° C.) for 28 days and measured according to the Japan Society of Geotechnical Standards “Unaxial compressive test method of soil”.

(2) Gelation time (A) Gelation time of homogel Measured by the cup inverted method at 20 ° C.

(B) Soil gelation time At 20 ° C., the grout solution is mixed with sand and allowed to stand still, the supernatant is discarded, and a bamboo skewer is stabbed into the sand to pull it out. Measurement.

(3) pH Measured with a glass electrode pH meter.

(4) Viscosity Measure with a B-type viscometer until the viscosity exceeds 100 cps.

(5) Soil gelation time reduction rate The ratio of the gelation time reduction in soil to the gelation time of homogel was calculated by the following formula and displayed.

[0032]

[Equation 1]

3. Example In producing an acidic silica sol composed of water glass and sulfuric acid, a sequestering agent and / or a phosphoric acid compound was used in combination. Table 1 shows the formulation examples and the pH of the formulation, the gelation time [homogel, soil (Toyoura sand, sea sand produced in Chiba Prefecture)], the gelation time reduction rate in soil, and the uniaxial compressive strength of sand gel.

Further, the change in viscosity at 20 ° C. was measured over time of the mixed solution, and the change in viscosity with respect to the elapsed time (ratio to gelation time) is shown in FIG.

[0035]

[Table 1]

In Table 1, Comparative Examples No. 1, 2, 4,
Reference numerals 5 and 7 are conventional acidic silica sols composed of water glass and sulfuric acid. As the content of water glass is higher and the pH is higher, the gelation time tends to be shorter as a matter of course.

In each of the comparative examples, a sequestering agent and / or a phosphoric acid compound is added to each comparative example.
The gelation time of the homogel is almost the same as the gelation time of the comparative example, and shows almost the same value.

However, the soil gelation time was extremely short in the comparative example, and the soil gelation time reduction rate was 97 to 98% for Toyoura sand and 99% or more for sea sand produced in Chiba prefecture. Very big.

In the examples corresponding to the respective comparative examples, however, it is as small as 61 to 93% in the case of Toyoura sand and 84 to 95% in the case of sea sand produced in Chiba prefecture. In particular, a system containing citric acid as a sequestering agent (Example No.
In No. 2, 6, 8, 10), Toura sand is 61 to 87%, and Chiba prefecture sea sand is 84 to 93%.

That is, although the conventional acidic silica sol itself depends on the SiO ₂ concentration and pH, the gelling time of the homogel is generally several hours to several days, but once this is injected into the soil. Soil gelation time is less than 1 minute to several tens.
It will be shortened to minutes.

Comparative Examples Nos. 3, 6 and 8 are sequestering agents for metal ions,
In the case of containing a phosphoric acid compound but having a high pH of 2.8 or higher, the shortening of the gelling time in soil is relatively small as in the present invention, but the gelling time of the homogel itself is shortened. Inevitably, gelation in soil is fast, and it takes less than 10 minutes in sea sand produced in Chiba Prefecture, which is not preferable because it is a little unstable for preventing liquefaction.

On the other hand, in the system of the present invention, the gelation time of the homogel is almost the same as that of the conventional acidic silica sol,
The soil gelation time is about several tens of minutes to 300 minutes.

Further, in the system of the present invention, although the gelling time in soil is long as described above, the strength thereof is almost the same as that of the conventional acidic silica sol, or rather slightly higher.

In FIG. 1, in the system according to the present invention, the concentration is almost in the range indicated by the solid line of the curve (a).
On the other hand, in the acidic silica sol of Comparative Example (excluding Comparative Examples Nos. 3, 6, and 8), the concentration is almost in the range shown by the dotted line of the curve (b), and the system according to the present invention is It was found that the viscosity was lower than that of the conventional acidic silica sol and gelation occurred.

In the above embodiment, the sequestering agent is
Take ethylenediaminetetraacetic acid, citric acid, sodium citrate, sodium hexametaphosphate, sodium acid pyrophosphate as an example, and phosphoric acid compounds other than condensed phosphates, such as phosphoric acid and sodium dihydrogenphosphate. However, of course, other sequestering agents and phosphoric acid compounds other than those described in the present text can obtain the same effects to a different degree.

From the above, the ground pouring grout material according to the present invention can greatly reduce the shortening of the gelation time in the ground, so that the gelation time in soil can be maintained for a long time and is relatively low until just before gelation. Viscosity is maintained, so it has excellent permeability and shows a consolidation strength that is more suitable than conventional acidic silica sols, and is particularly expected to improve large-capacity land by long-term continuous injection in ground liquefaction prevention work. I can play.

[0047]

The ground pouring grout material according to the present invention can exert the following effects.

1. Since the shortening of the gelation time in the ground can be reduced, the gelation time in the soil can be maintained for a long time.

2. Relatively low viscosity is maintained until just before gelation.

3. Despite the long gelation as described above, it exhibits a consolidation strength that is approximately suitable for conventional acidic silica sols.

Therefore, the ground-grouting material of the present invention is excellent as a ground liquefaction-preventing grout.

[Brief description of drawings]

FIG. 1 is a graph showing changes in viscosity with time after compounding a grout material of the present invention and an acidic silica sol of a comparative example.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-53588 (JP, A) JP-A-55-34201 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09K 17 / 46,17 / 48 E02D 3/12 C09K 103/00

Claims (2)

(57) [Claims] 1. An acidic silica sol composed of an acid and water glass is made to contain one or both of a sequestering agent and a phosphoric acid-based compound so that the pH value is 2.8 or less, and contacted with earth and sand in the ground. Even if the gelation time is shortened
To increase the gelation time in the soil and
It is possible to improve the large-capacity land and prevent liquefaction of the ground.
It is a grout material for ground injection. 2. The ground injection grout material according to claim 1, wherein the sequestering agent according to claim 1 is citric acid and / or a salt of citric acid.