JPH0237380B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ground consolidation method in which a consolidation liquid is injected into soft or leaking ground to consolidate or stop water (hereinafter simply referred to as consolidation), and in particular, a non-alkaline silicic acid aqueous solution is used as the consolidation liquid. Regarding the construction method, in detail, a non-alkaline silicic acid aqueous solution that can exhibit an arbitrary gelation time if the pH value is set to an arbitrary value in the acidic (5 or less) or neutral range (around 5 to 9) is used. Regarding construction methods. Conventionally, as a ground injection method using water glass,
Adding reactants to water glass was used. This utilizes the gelation of water glass in the alkaline region. However, with this method, the strength is several kg.
In order to obtain a consolidation strength of ~10/cm2 or ^higher , the water glass concentration must be increased, and as a result, the pH of the injection solution becomes around 12-11, which poses the problem of making the groundwater alkaline. arise. Furthermore, since unreacted water glass exists in the gel, leaching of unreacted water glass occurs over a long period of time, and as a result, the solidity cannot be expected to be permanent and its strength decreases over time. Problems also arise. Generally, when an acidic reactant aqueous solution is gradually added to a water glass aqueous solution while stirring, at the water glass concentration normally used for the injection method, gelation occurs when the pH is within the alkaline range, and the acidic reactant aqueous solution Even if it is added until the pH reaches 7 or acidic, the blended liquid becomes solidified and cannot maintain its fluidity. Of course, 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 of the consolidated sand decreases significantly and
Kg/ ^cm2 or less. The present inventor has already added and mixed water glass into an acidic reactant aqueous solution, removed the alkali in the water glass without causing the silicic acid content in the water glass to precipitate in lumps during mixing, and obtained a non-alkaline silicic acid aqueous solution. We have invented a ground injection method in which a non-alkaline silicic acid aqueous solution is adjusted to a predetermined pH value in the acidic or neutral range and then injected. This grout is very good because it does not change the PH value of the groundwater in the ground where it is injected, but when adjusting the gelation time, it is possible to shorten the gelation time by shifting the PH value from acidic to neutral. It is something to be measured. That is, as shown in Figure 1, first, water glass is added to an acidic liquid to create acidic water glass with a pH of around 1, and then an alkali is added to it to increase the pH value.
The PH value was set to around 8 or higher, and the gelation time was shortened before injection. In this case, as is clear from the curve in Figure 1, adjustment must be made on a sharp curve from an upwardly convex inflection curve (PH around 1) to a downwardly convex inflection curve (PH around 8). Therefore, there was a problem in that a slight difference in the amount of alkali added caused a wide difference in the gelation time. In other words, it is good to obtain a very short gelation time when the pH value is neutral between 5 and 8, but it is better to obtain a slow gelation time when the pH value is in the acidic region or in the neutral region. It was almost impossible. As a result of conducting research to solve these problems, the inventors of the present invention focused on the following points. In other words, neutral salts of alkaline metals and aluminum salts, which instantly precipitate silica in water glass even when added in small amounts to water glass in the alkaline range, cause clouding under certain conditions in the PH range of non-alkaline water glass. The present invention was completed based on the discovery that it can exist in a non-alkaline water glass aqueous solution without any formation, and has the effect of gently promoting gelation and increasing gelation strength. In order to achieve the above object, according to the present invention:
In the ground injection method of injecting non-alkaline water glass grout into the ground, the following (a) and (b) are added to the non-alkaline water glass grout in combination to gel the non-alkaline water glass grout. It is characterized by adjusting the time. (a) Water glass or alkaline salt. (b) 0.2 to 7% by weight of neutral salts of alkali metals and/or aluminum salts. Examples of metal salts in the present invention include neutral salts of alkali metals such as NaCl, Na ₂ SO ₄ , KCl,
Examples of aluminum salts such as K ₂ SO ₄ include aluminum chlorides and sulfates. When these salts are added to water glass in the alkaline range at a concentration of 20% to 60% by weight, which is the water glass concentration normally used in waterglass grout, they begin to become cloudy immediately when added in an amount of approximately 0.2% or more of the total solution. If it exceeds 1%, non-homogeneous precipitates will occur, making it impossible to obtain a solution-like formulation having a gelation time of at least several minutes. However, these salts are added to an acidic solution with water glass to remove the alkali in the water glass, resulting in an acidic water glass solution (non-alkaline water glass grout), which is a compounded solution that gels in any non-alkaline pH range. When the component (a) is present in the
When the amount of the salt blended is in the range of 0.2% to 7% by weight of the total blended solution, the blended solution can maintain a homogeneous solution state without any white precipitate, and gelation is gently promoted. It was also found that the strength due to gelation was greatly increased. It is unclear why the above metal salts immediately form a white precipitate in an alkaline region and do not form a white precipitate in a non-alkaline region when using the same concentration, but depending on the presence or absence of OH ions, the silicic acid in water glass and these The reaction of metal salts exhibits different behavior, and silicic acid and these metals react or bond slowly in a non-alkaline region, or polymerization of silicic acid occurs slowly, which causes gelation to occur slowly or strongly. It is thought that this helps form a gel. Furthermore, according to the inventor's experiments, no effect was observed when the content of the metal salt was less than 0.2% by weight of the total blended solution, whereas when it exceeded 7% by weight, the silicic acid content in the blended solution was It was found that a white precipitate immediately formed. An experimental example is shown below. Experiment-1 Make an acidic liquid using acids such as sulfuric acid and sulfate,
A non-alkaline silicic acid aqueous solution is prepared by mixing a water glass aqueous solution of n=3 with rapid stirring. The ratio of sulfuric acid (98%) and water glass (undiluted solution),
An experimental example of the relationship between the PH value of a non-alkaline silicic acid aqueous solution is as follows.

[Table] In this way, a non-alkaline silicic acid aqueous solution with any pH value can be prepared. However, in general, the gelation time of a non-alkaline silicic acid aqueous solution corresponds well to the pH, but the above α and
As is clear from the relationship between PH, it is almost impossible to accurately adjust the PH by adjusting the amounts of water glass and acidic reactant, and a slight difference in the amounts can cause the PH to fluctuate significantly. , therefore the gelation time tends to vary widely. In order to solve this problem, conventionally, the first step is to determine the approximate PH value by mainly measuring and mixing water glass and acidic reactants. On the other hand, in the second step, the gelation time was controlled mainly by controlling the pH while adding pH regulators such as water glass and alkaline salts. In contrast, in the present invention, gelation is controlled by adding the above-mentioned salt. According to this, the PH value hardly changes, so the gelation time can be controlled very easily. According to the method described above, sulfuric acid was used as the acidic agent, and as the first step, the water glass concentration was 40 wt% and the PH
After preparing a blended solution (solution A) with a pH of approximately 2.5 to 3.0, the second step is to slightly adjust the pH value using sodium bicarbonate or water glass, and to adjust the gelation time using the salt mentioned above. An example of controlling is shown below. Furthermore, the resulting mixed solution was used to solidify mountain sand, and the unconfined compressive strength was measured one week later. The experimental results are shown in Table-1 and Table-2.

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Claims (1)

[Scope of Claims] 1. In a ground injection method in which non-alkaline water glass grout is injected into the ground, the following (a) and (b) are contained in combination in the non-alkaline water glass grout, and the non-alkaline water glass grout is A ground injection method characterized by adjusting the gelation time of alkaline water glass grout. (a) Water glass or alkaline salt. (b) 0.2 to 7% by weight of neutral salts of alkali metals and/or aluminum salts.