JPS597750B2 - Ground injection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground injection method of injecting a consolidation liquid into soft or leaky ground to consolidate the ground, and particularly relates to a method using a non-alkaline silicic acid aqueous solution as the consolidation liquid. Specifically, by using an acidic silicic acid aqueous solution that satisfies certain conditions as a non-alkaline silicic acid aqueous solution, while injecting grout that itself exhibits an acidic value of PH5 or less, the pH value of groundwater is 5.8 to 5.8, which is the drainage standard value. This relates to an injection method that is excellent in maintaining the groundwater level in the construction area because it can keep the value within the range of 8.6.

As described above, the present invention is highly safe in terms of pollution, has excellent underwater solidification properties and durability, and can be used in combination with cement grout. This provides an extremely useful technique for injection construction, in that it can maintain sufficient gelation time, has excellent permeability, and can obtain high strength.

Conventionally, as a ground injection method using water glass, a method has been used that applies the phenomenon of gelation, in which gelation time decreases as a reactant is added to water glass.

Therefore, in such a method, the water glass itself is highly alkaline, and since it solidifies instantaneously when the pH is around weak alkalinity, the solidified material is also alkaline (usually around 12 to 10), and moreover, the water glass itself is highly alkaline. The problem arises of making alkaline. Furthermore, since unreacted water glass is present in the gel, leaching of unreacted water glass occurs over a long period of time.
For this reason, the permanence of the solidified body cannot be determined, and the problem arises that the strength decreases over time. When the acidic reactant aqueous solution is gradually added to the water glass aqueous solution while stirring, gelation occurs when the pH is within the alkaline range at the water glass concentration normally used for the injection method, and further acidic reactant aqueous solution is added. Even if you add it until the pH reaches 7 or acidic,
The blended liquid appears solidified and cannot maintain fluidity. However, by first preparing an aqueous acidic reactant solution and then mixing a water glass aqueous solution into the aqueous solution while stirring rapidly, it is possible to maintain sufficient fluidity while adding a sufficient amount of water glass, and to maintain sufficient fluidity over a specified period of time. It is possible to obtain a formulation that can later be gelled. The closer the pH value of the blended solution is to neutrality, the shorter the gelation time becomes. A water glass aqueous solution gels fastest when the pH is around 8, and the silica content therein becomes most unstable.

Therefore, when an acid is added to water glass to change it from alkaline to neutral to acidic, it becomes gelatinous or lumps of silica precipitate, resulting in an unstable state. Therefore, such grout is not suitable for injection because it does not have fluidity or causes clogging between soil particles, resulting in incomplete penetration.

On the other hand, in the method of adding water glass to an acidic solution to create an acidic silicic acid aqueous solution, the silicic acid content does not pass through the pH range of around 8, where it becomes most unstable, even if the silicic acid concentration is high. can maintain a stable solution state for several minutes. Furthermore, water glass grouts in the neutral range are also known. The basic idea behind water glass grout in the neutral range is that if neutral grout is injected to prevent alkali contamination of groundwater, the groundwater can also be kept neutral. However, as a result of various studies, the present inventor found that by using an acidic silicic acid aqueous solution under certain conditions, the groundwater in the injection area has P in the neutral range, even though the grout itself is acidic.
They discovered that it is possible to maintain the H value, and also invented a grout that has high strength and high permeability that cannot be obtained with water glass grout, which itself is in the neutral range.

That is, as a result of various studies, the present inventor has found that the properties of non-alkaline silicic acid aqueous solution as a pouring agent are simply due to the composition of water glass,
Focusing on the fact that these are not uniquely determined by concentration, pH, etc., but are comprehensively related, we calculated the factor related to H+U as X=?
Expressed as
It has been found that when the number is within the range of 6, extremely excellent characteristics can be exhibited as an injector, and the present invention has been completed.

As described above, the present invention is applicable to a ground injection method in which a non-alkaline silicic acid aqueous solution obtained by adding water glass to an acidic reactant aqueous solution is injected into soft or leaking ground to solidify the ground. It consists of using an acidic silicic acid aqueous solution that satisfies both the following requirements.

PH value must be approximately 5 or less.

Ta-4? ;The co-value is approximately 1 x 10-3 or less.

However, [H+] is the molar concentration of hydrogen ions, and [S
iO2] is the molar concentration of silicon dioxide and n is the molar ratio of water glass.

When gelling water glass is applied to ground injection, it is necessary that the means of ground injection be suitable for the purpose and be suitable for environmental conservation.To this end, the following requirements must be met: It is.

1. Since it is compatible with the injection method of mixing, injection operation, and penetration into the ground, it can take several tens of minutes to several hours to form a gel.

2. The viscosity can be maintained at around several Cp to 10 cp.

3. The pH of the injection solution can be accurately controlled.

2. , Since it can be applied to the purpose of consolidation, the uniaxial compressive strength is several K9/CT! Able to maintain strength of 1~101<g/d or more.

2. Excellent permanence with no decrease in strength over time.

3. Excellent solidification properties in water.

4.Do not impede the solidification of the pouring material used in combination, such as cement grout.

3. Good for environmental conservation and does not cause pollution.

1. Do not allow the water quality in the injection area to become alkaline or acidic beyond regulations.

2. It can be easily detected if it flows directly into the water supply.

Kg/C utilizing gelation of water glass in alkaline region
In order to obtain a consolidation strength higher than Tl, the water glass concentration must be increased, and as a result, the pH of the injection solution is 12~12.
11, and unreacted portions of water glass, which is the main component, were leached out, resulting in a problem that the strength decreased over time and that the surrounding groundwater tended to fluctuate towards the alkaline side.

Taking these points into consideration, the present inventor focused on applying gelation of a non-alkaline silicic acid aqueous solution to the injection method.

When gelation with a pH of around 5 to 8, which is almost neutral, is applied to injection, it is very good that the pH of groundwater does not change at all and the strength does not change over time. The unconfined compressive strength of only about 1 to 2 kg/d can be obtained, and the gelation time is limited to a very short period of several minutes after instant setting.

(Gelation time is particularly short in summer) If you try to increase the strength to 2 to 3k9/d or higher in gelation in the neutral region, the water glass concentration must be increased, and as a result, The gelation time becomes even shorter, and the fluidity of the injection solution in the ground cannot be maintained. Also, like this 1-2
Even if a strength of about k9/d is to be obtained, it must be injected in a short gelation time, so a highly acidic compounded solution is used as the A solution and an alkaline compounded solution is used as the B solution.
It is necessary to inject equal amounts of both liquids so that they meet at a certain ratio and inject to reach a neutral region, but it is difficult to achieve accurate merging due to errors in the injection operation. As usual, there is a problem that the pH value of the combined liquid fluctuates greatly between acidic and alkaline, and the gelation time also tends to vary. Furthermore, if the water glass concentration is made very dilute, the gelation time can be extended to several tens of minutes, but in this case, the strength decreases significantly to about 1k9/011 or less. In addition, if the injection is performed accurately by applying gelation in the neutral region, it is excellent in that it hardly changes the pH value of groundwater, but if it flows directly into a drinking well etc., the pH measurement will be difficult. There is a problem that cannot be easily detected depending on the method. In other words, it is natural that it is not preferable to use water that directly flows in for drinking even if the pH value itself is neutral, and the fact that this cannot be easily detected leaves a practical problem. . In this way, grout that utilizes gelation from weakly acidic (around 5) to neutral (up to around 8) is difficult to satisfy the elements of permeability and strength at the same time, and the gelation time is short, so the composition is changed to liquid A. The PH of the injection solution must be mixed separately, and the two solutions must be combined and injected.
There are problems such as the difficulty of accurately controlling the gelation time, and the difficulty of easily detecting the presence of water in water.

On the other hand, when focusing on the gelation of water glass in acidic regions, if an acidic silicic acid aqueous solution with a very low pH is used, there is a tendency for groundwater to become acidic. Although they are used together, there is also the problem of inhibiting the setting of cement.

However, if the pH is 5 or less and the above-mentioned X value is 10-3
It has been found that when gelation of an acidic silicic acid aqueous solution in the following range is applied to ground injection, all of the above-mentioned requirements for ground injection can be satisfied. In particular, it is possible to simultaneously satisfy good permeability and high strength by maintaining high strength with sufficient gelation time.

Even when used together with O-cement grout, its caking property is not impaired. ○There is very little tendency for the pH value of groundwater to be on the acid side, and the water quality standard value for groundwater is 5.8.
can be kept within a more neutral range.

○ Since a long gelation time can be obtained, it is possible to mix accurately in a mixer, the pH of the injection solution can be completely controlled, and the gelation time can be set accurately.

Since the O injection liquid itself has a pH of 5 or less, if it directly flows into water, it can be easily detected with a PH meter, dramatically increasing its practicality in terms of safety.

Such advantages cannot be obtained at all when the pH value of the acidic silicic acid aqueous solution is around 5 to 8, and when the pH value is below 10-3,
In particular, it can only be obtained within the range of 1 x 10-3 to 5 x 10-6.

The relationship between the aforementioned factors is shown in the drawing.

In the figure, the acidic reactant used is sulfuric acid.

However, basically any acidic reactant may be used, and no matter what kind of acidic reactant is used, almost the same tendency will be exhibited. Of course, strong acids are economically better. During actual injection, it is not only possible to directly adjust the gelation time according to the function shown in the drawing, but also to prepare an acidic silicic acid aqueous solution that gels over a long period of time beforehand. By applying this function, it is also possible to adjust the desired gelation time by adding a pH adjuster such as an alkaline agent. However, it goes without saying that adjustment is difficult depending on the size of the buffering effect. The figure shows the gelation time of an acidic silicic acid aqueous solution obtained by mixing various molar ratios of water glass in a sulfuric acid aqueous solution as an acidic reactant with rapid stirring, and the relationship H+J X=.

RO! 8) n Table 1 shows the PH, [H+], [S!] when using water glass with a molar ratio of 3.0. 02] The value of X corresponding to is displayed.

However, the water glass used is
Not only is this useful for setting gel time, but it is also closely related to the requirements for the injection method mentioned above.

That is, according to the research of the present inventor (1▲, X=1.

I... range of 1x10-3 or less, especially approximately 1x
Acidic silicic acid aqueous solutions that are between 10-3 and 5 x 10-6 and can gel themselves meet the requirements necessary for injection methods, especially the influence on the pH value of groundwater, underwater consolidation properties, and the permanence of consolidated bodies. It was found that it exhibits excellent properties in terms of sex and other characteristics. That is, as can be seen from the experimental results described later,
〉1×10-3, groundwater tends to become acidic,
In addition, it becomes inferior in terms of solidification properties in water. Moreover, the co-usability of cement becomes worse. Furthermore, in the case of X5x10-6, it becomes difficult to maintain the penetration time and the viscosity becomes high. That is, 1
×10-3> It exists within the range and can maintain permanence. Furthermore, even if the grout according to the present invention is injected after cement is injected, not only does it not impede the hardening of the cement, but even if cement is continuously injected before the grout has completely gelled, the cement will not function properly. Various combination methods of cement such as solidification are possible. According to the research of the present inventor, an acidic silicic acid aqueous solution has a pH of 11×10−3〉X〉5×10−2 from 2 to
It has been found that when the two conditions in the range of 5 are simultaneously satisfied, it has particularly excellent characteristics for ground injection, but even when the pH is more acidic than 2, it can be put to practical use if X is within the above range. Table 1 shows the results of experiments conducted by the present inventor, including several experimental examples described below. Table 1 middle thick line (the range surrounded by the double line is the range where the pH is more acidic than 5 and 1
The range of the acidic silicic acid aqueous solution is shown as x10-3>X>75x10-6. Experiment 1 An acidic solution is prepared using concentrated sulfuric acid as an acidic reactant, and an aqueous solution of n=3 water glass is mixed in with rapid stirring to produce an acidic silicic acid aqueous solution.

An experimental example of the relationship between the ratio of sulfuric acid (98%) and water glass (undiluted solution) and the pH value of an acidic silicic acid aqueous solution is as follows.

However, it is possible to make an acidic silicic acid aqueous solution with an arbitrary pH value in the range of 2 to 5 in this way, but the acidic silicic acid In order to make an aqueous solution practical as an injection method, the first step is to prepare a compounded solution with a long gelation time corresponding to the approximate pH value using a strong acid, and then the second step is injection. Immediately before inhalation into the pump, the pH is slightly adjusted using an alkaline or acidic agent to obtain a desired pH value, and a predetermined gelation time is obtained before injection.

In this case, the use of a weak alkali or weak acid facilitates fine adjustment of the pH. Usually, the most appropriate method is to prepare a highly acidic silicic acid aqueous solution and adjust the pH to an appropriate pH value with a weak alkali or water glass aqueous solution. This is because, as can be seen from the drawing, the gelation time of an acidic silicic acid aqueous solution corresponds well to the PH, but as is clear from the relationship between α and PH above, the PH depends on the amount of fluorophore glass and the acidic reactant. This is because it is almost impossible to accurately adjust the amount from the beginning, and a slight difference in the amount will cause the pH to fluctuate greatly and, therefore, the gelation time to vary widely. Therefore, in the first step, the approximate pH value is determined mainly by measuring and mixing the water glass and the acidic reactant. On the other hand, as shown in the drawing, taking advantage of the fact that the relationship between PH and gelation time can be obtained using X as a mediator, in the second step, the PH (111 constant The gelation time is managed mainly by controlling the pH using a container.Such a method makes it possible to concretely apply the gelation of an acidic silicic acid aqueous solution to ground injection.Following such a method, Using sulfuric acid as an acidic reactant within the SlO2 range classified below, the first step is to prepare a mixed solution with a pH of approximately 25, and the second step is to finely adjust the pH value using sodium bicarbonate. .

The resulting acidic silicic acid aqueous solution was used to solidify the mountain sand, and the unconfined compressive strength was measured after one week. Table 2 shows the gelation time and strength range corresponding to the SiO2 concentration (molar concentration) classification PH, [SlO2].

It can be seen that in the pH range of 5 or less, a region with a long gelation time and high strength exists.

Experiment 2 In order to find out how the pH value of groundwater changes when the present invention is implemented, the
Fill TIL's aquarium with mountain sand and keep the pH at 7 to a height of 20 meters.
Forms a groundwater layer with water, width 10 CTIL 1 length 30 cm
Mountain sand solidified with an acidic silicic acid aqueous solution having a TrL1 thickness of 20 CTfL was buried in the end of the mountain sand inside the water tank, and one week later, water from the other end was collected and the PH value was measured.

The acidic silicic acid aqueous solution was prepared according to Experiment 1. The following can be seen from Table 3. In other words, when an acidic silicic acid aqueous solution is injected, the groundwater shifts more or less to the acidic side, but it is closer to neutral than the value of the mixed solution, and the extent to which the groundwater shifts to the acidic side depends on the range of the PH value of the mixed solution. varies greatly depending on P
If the H value is 2 or less, the degree of acidity of the groundwater is high, but if the PH value of the mixed liquid is greater than 2, it is 5 or more, and especially if the PH value of the mixed liquid is 3 or more, the PH value is 6 or more. It can maintain a pH value of 5.8 or higher, which is the PH value required by groundwater water quality regulations. However, it can be seen that even if the pH is 2 or less, if X is within the above range, the degree to which the groundwater exhibits an acidic value is low.

From Table 3, it can be seen where the distribution of pH values of 5.8 or higher is located. Experiment 3 200 cc of the mixed solution was injected into the ground in the water tank used in Experiment 2 using a model injection device.

The mixed solution was prepared according to Experiment 1. After one week, the volume of the solidified material was measured, and when it was injected into the ground below the groundwater table, how many times the amount of compacted soil was compared to the amount of the mixed solution? The formation was measured and the results are shown in Table 4.

Table 4 shows that an excellent consolidation rate can be obtained when the pH value of the blended liquid is in the range of 2 to 5, preferably in the range of 3 to 5.

If the pH value is 2 or less, it is easily affected by groundwater, and P
When the H value is 5 or more, it is difficult to ensure sufficient penetration time, and it is considered that the amount of compacted soil is small. however,
It can be seen that even when the pH is between 1 and 2, the solidification rate is good as long as X is within the above range.

From Table 4, when injected into the ground below the groundwater table, the consolidation rate α
You can see where the distribution where is 2.5 or more is located. Experiment 4
An acidic silicic acid aqueous solution was prepared according to the method shown in Experiment 1, and the uniaxial compressive strength of the consolidated sand was measured over time using a specimen obtained by filling a mold with mountain sand and injecting it with a hand pump. .

Table 5 shows the formulation, initial viscosity, and unconfined compressive strength of the acidic silicic acid aqueous solution used for each specimen.

From Table 5, it can be seen that the viscosity of the compounded liquid is low, the strength increases over time, and the permanence is extremely excellent.

3.1 Acidic reactants in the present invention include acids such as inorganic acids (sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc.), organic acids (formic acid, acetic acid, etc.),
Acidic salts (monocalcium phosphate, monosodium phosphate, sodium hydrogen sulfate, aluminum sulfate, aluminum chloride, etc.), substances that generate acid groups by hydrolysis in the presence of alkali (esters such as polyhydric alcohol acetate) , ethylene carbonate, α-butyl lactone, etc.; aldehydes such as glyoxal; amides such as formamide).

Although the above examples are shown, it goes without saying that the present invention is not limited to these examples.

In addition, as a pH adjusting agent or a gelling time adjusting agent, salts (inorganic salts, organic salts, basic salts, neutral salts, acid salts, etc.), alcohols, alkalis such as caustic soda, etc. are used as shown in the examples below. , can be used to react with silicic acid, or to
or by other chemical or electrochemical actions, those that cause the formation of silicic acid gel, vary the gelation time, vary the fluidity, or increase the caking property. To tell.

The following example shows an example, and is not limited to these. Inorganic salts: acidic salts, neutral salts, basic salts such as calcium chloride, sodium chloride, magnesium chloride,
Chlorides such as potassium chloride and aluminum chloride, sulfates such as calcium sulfate, sodium sulfate and aluminum sulfate, aluminates such as sodium aluminate and potassium aluminate, hydrochlorides such as ammonium chloride, zinc chloride and aluminum chloride, chlorine acid sodium, potassium chlorate,
Chlorates such as sodium perchlorate and potassium perchlorate, sodium carbonate, potassium carbonate, ammonium carbonate,
Carbonates such as sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, sodium bisulfate, potassium bisulfate,
Bisulfates such as ammonium bisulfate, bisulfites such as sodium bisulfite, potassium bisulfite, ammonium bisulfite, silicates such as sodium silicate, potassium silicate, alkali metal salts of silicic acid, alkaline earth metal salts, aluminum Silicates such as salts, borates such as sodium borate, potassium borate, ammonium borate, hydrogen phosphates such as sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, sodium pyrosulfate, pyrosulfate Potassium, pyrosulfates such as ammonium pyrosulfate, pyrophosphates such as sodium pyrophosphate, potassium pyrophosphate, ammonium pyrophosphate, dichromates such as sodium dichromate, potassium dichromate, ammonium dichromate, permanganese acid potash,
Permanganates such as sodium permanganate.

Organic salts: Sodium acetate, sodium succinate, potassium formate, sodium formate, etc.

In addition to acting as a pH adjuster or gelling time adjuster, these also have the effect of a strength enhancer.

Furthermore, the above-mentioned acids, acidic silicic acid aqueous solution, and water glass can also be used as pH adjusters.

In particular, agents that act as weak alkalinizers are effective in adjusting the pH. Furthermore, the water glass in the present invention may include any molar water glass having a molar ratio n (SlO2/M2O) of 1.5 to 5.0 including liquid water glass, anhydrous water glass, hydrohydrated water glass, crystalline water glass, etc. An alkali metal salt of silicic acid or a mixture of an alkali metal salt of silicic acid and silicic acid is used.

In addition, since the acidic silicic acid aqueous solution in the present invention has a pH of 5 or less and an X value of 10-3 or less, it has low corrosivity.

Furthermore, if a rust preventive agent is mixed into the aqueous solution, corrosion hardly occurs. Incidentally, bentonite or any other clay may be mixed into the above-mentioned liquid mixture in any proportion.

In addition, the acidic silicic acid aqueous solution within the above range is used as the A liquid, and without the gelling modifier, cement, slag, etc. are added as the B liquid, and after combining and injecting the A and B liquids, only the A liquid is added. Continuous injection is also possible. In the injection according to the present invention, an aqueous solution of water glass is mixed into an aqueous solution of an acidic reactant in a mixer while it is rotated at high speed to create a non-alkaline silicic acid aqueous solution having a long gelation time and having an approximately predetermined pH value. Add a PH adjuster so that the pH is 5 or less and the X value is 10
It is injected after adjusting to an accurate predetermined pH value within the range of -3 or less, and the injection solution is accurately mixed in a mixer and can be injected with one injection pump (single shot injection method).
This is a big advantage, but of course using two pumps,
Non-alkaline silicic acid aqueous solution or its pH as liquid A
It is also possible to prepare an aqueous solution to which a regulator or strength enhancer has been added, prepare an aqueous solution of a PH regulator as the B solution, and then inject both A and B so that they meet the desired pH value. ,A
Prepare a water glass aqueous solution as the liquid and an acidic reactant dissolved in water as the B liquid, or an aqueous solution to which a PH adjuster or strength enhancer is added, and combine the A and B liquids to obtain a predetermined pH value. It can also be injected into. However, if the silicic acid concentration is high, the pH will vary due to variations in the discharge amounts of liquids A and B, resulting in no gelation at all, instant setting, or variation in gelation time.

However, if the silicic acid concentration is low, it is possible to use a method in which the water glass aqueous solution and the acidic liquid are combined through a pipe system. The method of adding acid to a water glass aqueous solution to lower the pH starts with adding acid to an excess of water glass.
In the method of merging and mixing so that the acidic region is 5 or less, an excess of acidic liquid and an insufficient amount of water glass merge, resulting in a state in which water glass is added to the acid, and a neutralizing effect takes place in the acidic region from the beginning. Therefore, as long as the merging operation is performed accurately, a stable acidic silicic acid aqueous solution can be obtained. On the other hand, first prepare an acidic silicic acid aqueous solution that can gel in the approximate pH range of 5 or less as solution A, prepare an aqueous solution of a pH adjuster as solution B, and combine solutions A and B to adjust the pH. The method of injecting to a predetermined PH value within the range of 5 or less and the Reliable solidification can be expected. Furthermore, it is also possible to create a composite ground by continuously injecting grouts with different gelling times and setting properties by continuously injecting the combined injection method and the one-shot injection method described above. The method that can most accurately set the pH value and accurately maintain the gelation time is to use a formulation that requires a long gelation time and adjust the pH value accurately in a mixer to a predetermined pH value. This makes such a method possible.

In addition, any injection tube can be used, such as a single strainer tube, a double strainer tube, or a rod.When injecting liquids A and B together, there is no need to use a strainer at either the tip or the end of the injection tube. but,
It goes without saying that the soil may be joined through a pipe system including a mixer before flowing into the injection pump, or that the soil may be injected while stirring and mixing the soil in the ground.

In addition, the injection pressure will move up and down even if it is injected at normal pressure, even if it is injected at a high pressure of several + K9/CTil to several thousand 1 < g/d, and even if it is injected with the injection tube fixed. The injection may be carried out while rotating or may be carried out while rotating. Example
1 Test injection was conducted in a soil layer below the groundwater table in fine sandy ground in the Tokyo area.

The injection solution was prepared according to the method in Experiment 1, using marrow acid as the acidic reactant and setting [SlO2] = 2.04. First, an acidic silicic acid aqueous solution with pH + 2.4 (α = 0.16) was prepared. Then, using sodium bicarbonate as a pH adjuster, the pH was adjusted accurately in a mixer to 3.2 (gelation time approximately 60 minutes), and this mixed solution was mixed with 3,000 ml of sodium bicarbonate.
Injected. Before, during, and after the injection, groundwater was sampled from a test hole 5 m away from the injection point and the pH was measured. P.H.
The measurement results are as follows. The on-site permeability test results were k = 6.8 x 10'''3CT!L/Sec before injection, but k = 8.3 x 10-6CTrL after injection. /S
ec was shown. Furthermore, when excavation was carried out one week after the completion of the injection, the soil was consolidated with a diameter of 2.5 m around the injection pipe, and an amount of consolidated soil of approximately 10 m3 was obtained. In addition, the consolidated sample specimen exhibited an unconfined compressive strength of Qu = 12.5 U.Example 2 Test injection was performed using a single hacker injection method in water stoppage work on rock with minute cracks.

Solution A was prepared according to the method in Experiment 1, using sulfuric acid as the acidic reactant, [SiO2] -1.36, and first preparing an acidic silicic acid aqueous solution with pH + 3.0 (α = 0.157). Using sodium bicarbonate as a pH adjuster, the pH was adjusted to 3.5 (gelation time: 30 minutes). After injecting a predetermined amount of liquid A, cement milk (300 kg of blast furnace cement, 301<g of bentonite, and 50 kg of slaked lime per M3) was continuously injected as liquid B from the same injection pipe.

The ratio (volume ratio) of the amounts of acidic silicic acid aqueous solution and cement milk injected per hole was approximately 2 for the former and 1 for the latter. The water permeability test results before and after injection showed that k-2.
5X10-3CTrL/Sec, k=4,
It showed 1×10-J gill `ec.

When we excavated and investigated the infiltration situation, we found that the gel had penetrated into the fine cracks, and the cement milk had penetrated into the coarse cracks, solidifying it firmly. In addition, when we measured the pH value of the drainage water during excavation, the pH value was approximately 6.5, which was lower than before injection.
Almost no change in H value was observed.

[Brief explanation of the drawing]

The drawing is a graph showing the relationship between gelation (11 hours and ?) of an acidic silicic acid aqueous solution in the present invention.

Claims (1)

[Scope of Claims] 1. In a ground injection method in which a non-alkaline silicic acid aqueous solution obtained by adding water glass to an acidic reactant aqueous solution is injected into soft or leaking ground to solidify the ground, the non-alkaline silicic acid aqueous solution is A ground injection method characterized by using an acidic silicic acid aqueous solution adjusted to satisfy both the following conditions [A] and [B]. [A] The PH value is approximately 5 or less. [B] [H^+]/[SiO_2]^n value is approximately 1×1
Must be 0^-^3 or less. However, [H^+] is the molar concentration of hydrogen ions, and [H^+] is the molar concentration of hydrogen ions.
SiO_2] is the molar concentration of silicon dioxide, and n is the molar ratio of water glass. 2. In the ground injection method according to claim 1, the pH value of the acidic silicic acid aqueous solution is first adjusted to an approximate value of 5 or less, and then a PH adjuster is added to the aqueous solution to form the above [A]. and a method of fine adjustment to a predetermined value that satisfies the conditions [B]. 3. The ground injection method according to claim 1 or 2, in which the acidic silicic acid aqueous solution is mixed with a pH adjuster and then injected. 4. In the ground injection method according to claim 1, the acidic silicic acid aqueous solution is obtained by combining a water glass aqueous solution and an excess acidic reactant.