JPS5993787A - Solidification of ground - Google Patents

Abstract

PURPOSE:To solidify the ground in a short gelling time and to strength it permanently without causing dispersion and scattering, by blending a colloidal solution of silicic acid with an alkali metal salt, etc. CONSTITUTION:(A) A colloidal solution of silicic acid is blended with (B) an alkaline(earth) metal salt or aluminum salt, and the blend whose gelling time is adjusted to <=20hr in impregnated into the ground. While it is impregnated, it becomes unstable, the gelling is accelerated, and it is solidified. The component A, from which Na ion is almost separated and removed, whose pH is usually adjusted to 8-10, SiO2 concentration to 10-60wt%, and Na2O to 0.01- 4wt%, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground injection method using a colloidal solution of silicic acid.

Traditionally, water glass grout has been used for ground injection. Water glass grout is a liquid alkali metal salt of silicic acid, and is used to solidify the ground by adding salt or acid to precipitate a silicic acid gel.

However, since the alkali metal salt of silicic acid exhibits high alkalinity and gelation occurs in the alkali region, there has been a problem that groundwater remains alkaline for a long period of time.

To solve this problem, a ground injection method has been developed in which water glass is added to an acidic solution and the alkali in the water glass is removed, and the alkali is combined with the acidic silicic acid solution to form a gel in a neutral region. There is.

This grout is a grouting material with extremely excellent properties, as the solids are neutral and the pH of groundwater does not change.
It had the disadvantages of low strength and very short gelation time.

That is, SiO is usually present in the injection liquid in water glass grout.
The concentration of SiO2 must be at least 10% by weight from the viewpoint of strength (uniaxial compressive strength of consolidated sand of 1kg/cm2 or more), but if the concentration of SiO2 is at least 10% by weight, the gelation time becomes neutral. In the vicinity of the area (PH 4 to 8), it fades within 1 minute, usually several seconds. It has been empirically determined that the gelation time is 30 to 120 minutes, which is suitable for good permeability and solidification without dispersing in the ground. If you want to get about 30 to 120 minutes, use SiO2
The concentration of sand must be 5% by weight or less, and at this concentration, the consolidated sand strength does not even reach 0.5 kg/cm2, making it practically unusable for the injection method. In addition, water glass grout in the neutral range is obtained by adding water glass to an acidic solution and neutralizing the alkali in the water glass to obtain the injection solution. A large amount of neutralized products such as Na ions and acid radicals remain, but from the viewpoint of water quality conservation, it would be better if an injection method could be established that does not leave any Na ions or acid radicals.

Another known method is to add water glass to an acidic solution and use it in the ground injection method. This method utilizes the phenomenon of gelation through silicic acid, and in order to obtain a formulation with SiO2 of 10 wt% or more and a long gelation time of 30 minutes or more, the pH must be 3.
It is necessary to adjust the injection to the nearby acidic area.

The present invention provides a further developed technique to solve the above problems.

That is, the present invention mixes a colloidal solution of silicic acid and a salt selected from alkali metal salts, alkali metal salts, and aluminum salts, and injects into the ground an injection solution prepared by adjusting the gelation time to within 20 hours. This solves the above problem.

The colloidal solution of silicic acid (silica sol) in the present invention is obtained by removing most of the alkali metal ions from a liquid aqueous alkali metal silicate solution (water glass), and includes, for example, a zeolite cation exchanger, Water glass is passed through an ion exchange resin such as an ammonium-based ion exchanger, and the generated silica sol is
The silica sol is further added to water glass at a temperature of .degree. C. to 90.degree. C. and passed through the ion exchange resin again for ion exchange, yielding a relatively pure (dilute) silica sol. In order to obtain even pure silica sol, the dilute silica sol mentioned above is adjusted to be slightly alkaline, and the above-mentioned silica sol is further added to it while evaporating, thereby simultaneously stabilizing and concentrating it. Alternatively, the activated silica sol after ion exchange can be used. A method is used in which the mixture is heated under a suitable alkali and activated silica sol is further added thereto for stabilization.

The silicic acid colloidal solution used in the present invention is procured to have a slightly alkaline pH of 8 to 10 or less, with most of the Na ions being separated and removed, with SiO2 being 10 to 60 wt% and Na2O being 4 wt%.
The amount adjusted to a range of t% to 0.01wt% is used.

When the Na2O content exceeds 4%, the silicate colloid dissolves and becomes an aqueous solution of silicate. On the other hand, Na2O is 0.
If it is less than 0.01%, the silicic acid colloid cannot exist stably and will aggregate. That is, Na2O is 4wt% to 0.01w
Na ions are distributed on the surface of the silicic acid colloid within a range of t% and can maintain a stable colloidal state. In this case, the grain size of the silicic acid colloid is mainly about 6 to 50 μm. If the particle size of the silicic acid colloid is 50 μm or more, it will precipitate. Further, the above silicic acid colloid has a molar ratio (SiO2/Na2O) of about 1000 to 10, and a pH of 8 to 10, which is desirable for stability of the colloid.

Further, it is desirable that the concentration of SiO2 is 60 to 10% by weight from the viewpoint of solidification strength as an injection liquid.

The silicic acid colloid prepared in this way is stable semi-permanently, and when used as an injection solution, there is no risk of gelation during transportation from the factory to the site or during injection operations. Even if this colloidal solution of silicic acid is directly injected into the ground, it will not gel itself within a practical period of time, so no practical consolidation effect will be obtained.

FIG. 1 shows the relationship between PH and gelation time according to experiments conducted by the present inventor.

Curve 1 shows the case of silicic acid colloid containing 30 wt% as shown in Table 2, and curve 2 shows the case of silicic acid colloid containing 30 wt% shown in Table 2, and curve 2 shows the case of adding and mixing water glass with a molar ratio of 3.4 to a sulfuric acid aqueous solution to make the SiO2 concentration 30 wt%. That's what I got.

As can be seen from this, when adjusting the pH value of ordinary liquid water glass, the relationship between pH and gelation time is the shortest when the pH is around 8.
While it is not possible to obtain a gelation time long enough for penetration into soil particles while maintaining the O2 concentration, when adjusting the pH value of silicate colloid, the gelation time is shortened when the pH is around 5 to 6. It can be seen that the gelation time is the shortest, and that a long gelation time can be obtained while maintaining a sufficient SiO2 concentration in the neutral region.

However, when the silicic acid colloid and the salt are added and the gelation time is adjusted to within 20 hours and then injected into the ground, the silicic acid colloid becomes unstable during the process of penetrating into the ground, and gelation occurs. promotes solidification without dispersion or dissipation.

Moreover, the gelation time can be easily adjusted from several seconds to 20 hours in an almost neutral range while maintaining a SiO2 concentration that provides sufficient consolidation strength.

The experimental results according to the present invention are shown in Table 1 below.

The silicic acid colloids used are shown in Table 2.

Table-1 Table-2 Silicic acid colloidal solution used in the experiment From Table-2, a silicic acid colloidal solution and a salt selected from alkali metal salts, alkaline earth metal salts, and aluminum salts were mixed to form a weakly alkaline to weakly acidic region. It can be seen that gelation can be achieved at pH 4 to 8.

Among these salts, when an alkali metal salt is used, especially when a neutral alkali metal salt is used, the gelation time can be adjusted very smoothly and homogeneous gelation can be obtained.

In the case of alkaline earth metals, partial precipitation or partial gelation tends to occur, but gelation occurs as a whole. Aluminum salt precipitates and it is difficult to form a homogeneous gel, but when an acid and a small amount of aluminum salt are used in combination, the gelation time can be very effectively adjusted and homogeneous gelation can be obtained.

It is also understood that by using an acid and a salt in combination, the gelation time can be freely adjusted from several tens of minutes to several seconds in a weakly acidic to neutral range (pH around 4 to 8). Even if you try to adjust the gelation time using only acid, the gelation time will be 4.
It is difficult to shorten the time within that time.

The grout used in the present invention promotes gelation in the ground as described above, and has the property of being difficult to deviate from. Grout can be used as a secondary grout and is injected after the primary grout has previously been injected into the injection area.

As the above-mentioned primary injection material, one containing an electrolyte substance that dissociates calcium ions is particularly good, and one or more of lime, cement, calcium carbonate, gypsum, calcium chloride, etc. can be used in combination with this. Of these, except for cement, they do not have the ability to solidify by themselves. Therefore, it is important to securely fix the injection target area. Of course, even if cement is used, it is necessary to securely fix the cement to each injection stage.

In order to solve the above problems, it is desirable to use the primary injection material in combination with cement injection, or to give it solidification properties.

For example, when initially injecting lime, lime, calcium carbonate, or calcium chloride may be mixed with cement, or cement may be injected in advance and then lime, calcium carbonate, or calcium chloride may be injected, or lime may be mixed with gypsum or calcium chloride. It is possible to use methods such as adding slag, fly ash, etc. to give it solidification ability. Alternatively, water glass grout containing these components can also be used.

In addition, in order to reliably distribute these primary injection materials in each injection stage in advance, the primary injection materials must be poured into the ground through an injection pipe (Figure 2) that has a discharge port that can be re-injected to a predetermined depth of the injection pipe. Either inject the secondary injection material in a layered manner after injecting the material, or use a multi-pipe rod to overlap the secondary injection material before the primary injection material injected dissipates outside the designated area. You can take the injection method. (
Figure 3).

Referring to FIG. 2, first, an injection hole 1 is drilled in a predetermined ground and a casing 2 is inserted. Next, after inserting the injection pipe 5 surrounded by the rubber 4 into the discharge hole 3, the space between the casing 2 and the injection pipe 5 is sealed with the sleep grout 6, and the casing 2 is pulled out.

Then, a strainer pipe 8 provided with a packer 7 is inserted into the injection pipe 5, and a primary grout injection agent is injected from an injection pump (not shown). Then, after this injection is completed, a secondary grouting agent is injected.

To explain FIG. 3, FIG. 3(a) shows a situation in which a double pipe is used to send polling water from the lower discharge port 12 of the inner pipe 10 to drill a hole to a predetermined depth.

13 is a metal crown. Thereafter, as shown in FIG. 3(b), the primary injection material is sent through the outer pipe 9 and injected into the ground through the upper outlet 11, while the secondary injection material is sent through the inner pipe 10 and into the ground through the lower outlet 12. By moving from the bottom to the top of the injection stage while injecting, the secondary injection material is injected overlappingly into the area where the primary injection material has been injected.

In the present invention, a silicic acid colloid having a pH of 8 to 10 is normally used, but a silicic acid colloid having a pH of more than 4 may be used and the above-mentioned salt may be added thereto.

In the following description, the reason why it is desirable that the gelation time of the injection liquid injected into the ground is usually within 2 hours is as follows.

Inject into the ground from the tip of the injection pipe, 1m in diameter from the injection hole.
When the area is consolidated, the amount of consolidated soil is 4/3×π×1≒4m
It is 3.

Assuming that the porosity of 1 m3 of sand is 0.4, empirically the porosity of 80
% is filled with the injection liquid and the sand solidifies, the amount of injection required per 4 m3 is 4 x 0.4 x 0.8 = 1.28 m3 = 1280 liters, and if the injection amount per minute is 10 liters, the radius is 1 m. The injection time to infiltrate the injection liquid into the spherical shape is 1280÷10=128
It will be a minute.

Therefore, if the initially injected injection liquid loses its fluidity within approximately 2 hours, the injection liquid will not disperse or escape and the diameter will be approximately 2 hours.
This results in homogeneous solidification over a certain range of m.

The above is an example of the ground that is the target of normal injection, and if a diameter of 2 m can be solidified there, a sufficiently satisfactory effect can be achieved. Therefore, the above conditions are sufficient conditions to achieve the injection effect in general injection work. You can take a look.

Based on this idea, we conducted the following experiment.

Experiment 1 The bottom end of a vinyl pipe with a cross-sectional area of 10 cm2 was closed with a stopper, and the bottom 1 m length was filled with sand from Chiba Prefecture. Increase the porosity of sand to 40
320 cc (10 x 100 x 0.4 x 0.8 = 320 cm3 porosity = 0.4, gap filling rate 0.8) of the blended liquid was poured into the tube, with the gap filling rate of the injection liquid being 80%.

The blended solution was prepared with the following gelation time based on Table 1.

Table 3 Ten samples of the above-mentioned vinyl tubes filled with sand were prepared.
After 120 minutes after pouring the above-mentioned liquid mixture, the stopper at the bottom end of the vinyl tube was removed, and it was examined whether the injection liquid would flow down or not.

No. It was found that the solutions using formulations Nos. 32, 5, 6, and 10 did not flow down and did not gel at the top, but did gel at the bottom. Also, No. 1, 4, 24,
The mixture using No. 18 did not flow down and the upper part was also gelled. Also No. In the cases where the mixed solutions No. 30 and 31 were used, the mixed solution flowed down without gelling together with the sand.

As a result, when a material whose gelation time was adjusted to within 20 hours was injected into the ground, gelation was accelerated during the injection process,
It was found that fluidity was lost within approximately 20 hours.

In the present invention, the alkaline earth metal salt does not contain cement, because although cement contains Ca ions, it has a large particle size, and the silicate colloid and cement particles combine to form a floc and penetrate. This is because the tofu becomes difficult to cook and becomes crumbled, making it unsuitable for injection. Although alkalis such as lime and gypsum agents are poorly soluble, they can form a homogeneous gel by adjusting the amount. Therefore, in the present invention, hydroxides of alkaline earth metals are also included in alkaline earth metals. Similarly, aluminum hydroxide is also included in aluminum salt.

Furthermore, the present invention requires that a reactant containing one or more of alkali metal salts, alkaline earth metal salts, and aluminum salts as an active ingredient be added to the silicate colloid, but any salts or Of course, acids and other compounds may be added. The acids include inorganic acids, organic acids, and those that act as acids when hydrolyzed, such as glyoxal and esters.

The vinyl pipe filled with compacted sand mentioned above is 10c as it is.
It was cut into m lengths, cured in a plastic bag, and one week later, the solidified body was pulled out from the vinyl tube and cured in water. The strength over time was measured. Table 4 shows the results.

As can be seen from the above, most of the gelling times within 20 hours showed an increase in strength, and those with a pH of 7 to 4 showed a remarkable increase in strength. In addition, it was found that the strength of those with a gelation time of 20 hours or more tends to decrease slightly over time. From this, it was found that those with a gelation time of less than 20 hours had excellent permanence.

Table-4 Strength of consolidated sand after curing in water Examples of the present invention will be shown below.

〔Example〕

A mixed solution using silicate colloid was applied to sandy ground in Tokyo.
00L was injected, a water permeability test was conducted, and the first direction was excavated to examine the consolidation status and the unconfined compressive strength of the specimen.

The results are shown in Table-5.

Table 5 From the above, it can be seen that when the gelation time is within 20 hours, relatively spherical solids can be obtained, and the strength and permeability coefficient are greatly improved.

On the other hand, if the gelation time is longer than 20 hours, the injected liquid will disperse and dissipate, and the injected liquid will not stay in the designated area, or it will solidify while escaping, and it will not be sufficiently filled between the soil particles. It can be seen that it is difficult to obtain a sufficient injection effect due to low strength or insufficient improvement in water permeability.

[Brief explanation of drawings]

Fig. 1 shows a graph of the relationship between pH and gelation time, Figs. 2 and 3 both show a specific example of an injection pipe for carrying out the method of the present invention, and Figs. b) shows a process diagram of the construction method of the present invention. 1... Injection hole, 3... Discharge port, 5... Injection pipe, 9... Outer pipe, 10
...inner pipe, 11...upper discharge port, 12...lower discharge port. Patent applicant Reinforced Soil Engineering Co., Ltd. Agent
Patent Attorney Hitoshi Someya

Claims (1)

[Claims] A soil solidification method characterized by injecting into the ground an injection solution prepared by mixing a colloidal solution of silicic acid and a salt selected from alkali metal salts, alkaline earth metal salts, and aluminum salts and adjusting the gelation time to within 20 hours. How to tie.