JPS636594B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ground improvement method using an improved alkali silicate (water glass) grout. Conventionally, chemical injection methods have been known in which various chemical solutions are injected into the ground and gelled in the ground in order to strengthen soft ground or stop water from spring water. Water glass grout, which has a gelling agent added to it as a main ingredient, has been widely put into practical use. In the chemical injection method, there has recently been a demand for instant setting type grout with a gel time of several seconds to several tens of seconds, which means that conventional grouts with a gel time of several minutes to several tens of minutes are difficult to install in places with a lot of underground water flow or in strata with a lot of sand and gravel. This is because when used, the chemical solution may be diluted and flowed out before gelatinization, or the chemical solution may penetrate into unnecessary areas, resulting in incomplete ground improvement and adverse effects on pollution. However, instant setting type grout has an unstable gel time and tends to partially gel, resulting in an uneven gel that often causes cloudiness and gel-liquid separation. Therefore, it becomes difficult to adjust the gel time, which causes a decrease in the strength of the injection ground. This tendency is particularly strong in the summer as the water temperature rises. In short, it is necessary not only to have a short gel time, but also to be able to form a uniform gel with a stable gel time throughout the year in order to improve soil quality. If only alkali bicarbonate is used as a gelling agent for soil stabilization, the infiltrated gel will shrink over time and the volume of the soil layer will not change, so the soil layer will become porous and its watertightness will decrease, as well as the infiltration. The gel component dissolves in the water and becomes brittle, resulting in a sudden drop in strength in water. The present invention uses water glass and its gelling agent to stabilize soil, and uses alkali bicarbonate as the main ingredient of the gelling agent, and uses this together with magnesium salt and tetrapolyphosphate to stabilize the soil. The object of the present invention is to provide a method for gelling and improving the above-mentioned decrease in shrinkage and strength in water. Furthermore, sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, potassium sulfite,
By also using inorganic salts selected from potassium carbonate, sodium sulfate, and potassium nitrate, we can provide a safe and inexpensive inorganic ground improvement method that enables more rapid and stable gelation. That is. That is, the first invention comprises (a) an aqueous alkali silicate solution with a solid content of 10 to 40% by weight, (b) 30 to 100% of sodium bicarbonate as a gelling agent.
5 to 25 parts by weight of magnesium sulfate or chloride alone or as a mixture to 100 parts by weight of alkali bicarbonate consisting of 0 to 70 weight % of potassium bicarbonate.
parts by weight, and 5 parts by weight of sodium tetrapolyphosphate
This is a ground improvement method characterized by injecting the above (a) and (b) into the ground and hardening it. In addition, in the second invention, when the above (a) and (b) are injected into the ground and hardened, the solution (a) is preliminarily mixed with potassium chloride, sodium chloride, potassium carbonate, potassium sulfite, potassium sulfate, sodium sulfate, or potassium sulfate. 0.1 to 5 parts by weight per 100 parts by weight of liquid (a), and/or
It is characterized in that 1 to 40 parts by weight of any one of sodium chloride, sodium sulfate, potassium sulfate, potassium sulfite, or sodium nitrate is added to the liquid (b) in advance per 100 parts by weight of alkali bicarbonate in the liquid (b). This is a ground improvement method. In an attempt to improve the shrinkage when alkali bicarbonate is used as a gelling agent, a two-component system using a magnesium salt in combination is known (Japanese Patent Publications No. 43247-1982 and Japanese Patent Publication No. 21778-56). However, using only magnesium salt tends to cause non-uniform gelation and is not suitable for use at high liquid temperatures in summer. Therefore, when magnesium salt is incorporated in a large enough amount to be effective in improving shrinkage, cooling is required or use is limited to special regions such as cold regions. Furthermore, Japanese Patent Publication No. 56-35709 describes the use of sodium bicarbonate, magnesium sulfate, and sodium chloride in combination. This type generally shortens the gel time, but a stable gelled product cannot be obtained unless the concentration of the gelling agent is lowered. If the concentration is low, the gel time will be long, and there is a risk that the injected chemical solution will be diluted and leaked out due to groundwater existing in the ground. Therefore, in order to use the gelling agent without diluting it, it is necessary to reduce the amount added, and in this case, the effect of an instant setting type with a gel time of several seconds cannot be desired. In addition, in order to stably dissolve polyvalent metal salts such as aluminum, magnesium, and iron in water, tartaric acid, EDTA,
It is also known to add chelating agents such as NTA and sodium tripolyphosphate, but in cases where the concentration of polyvalent metal ions is high, such as in grout gelling agents, even if known chelating agents are added, polyvalent metal It is difficult to completely dissolve and stabilize salts. Japanese Patent Publication No. 53-24724 describes the use of organic acids such as citric acid together with aluminum salts and magnesium salts, but when used in combination with alkali bicarbonate, the gelling agent solution foams, and if used as is, it will not work. I can not use it. Also, in general, when organic acids are used, COD
The load on construction sites is increasing, and surrounding groundwater is constantly being drained at the construction site.
It will also be necessary to observe COD. The present invention was made based on the knowledge that the above-mentioned drawbacks can be overcome by making use of the advantages of alkali bicarbonate and magnesium salts as gelling agents, and particularly by selecting sodium tetrapolyphosphate as a chelating agent. The alkali silicate used in the present invention is
The molar ratio of SiO ₂ /M ₂ O (M is an alkali metal) is 1 to
Sodium silicate or potassium silicate of No. 4 is preferred, and from the viewpoint of performance and economy, SiO ₂ /
Particularly preferred is an aqueous sodium silicate solution with a Ma ₂ O molar ratio of 2 to 3.5. The concentration of alkali silicate is
A solid content of Na ₂ O and SiO ₂ of 10 to 40% by weight is preferred.
If it is less than 40% by weight, the consolidation strength will not be sufficient, and if it exceeds 40% by weight, the viscosity will increase and there will be a problem in terms of permeability into the ground. Generally, a solution prepared by diluting sodium silicate of JIS No. 3 composition with water to twice the volume ratio is used. The alkali bicarbonate used in the gelling agent of the present invention is sodium bicarbonate alone or a mixture with potassium bicarbonate containing 30% by weight or more of sodium bicarbonate. If the sodium bicarbonate content is less than 30% by weight, a precipitate is likely to form when the gelling agent component is dissolved in water, and when mixed with an alkali silicate, it tends to flash cloudy and become unstable gel. . Magnesium sulfate and magnesium chloride are used as the magnesium salt, and magnesium sulfate is preferably used in view of the physical properties of the resulting gel, such as compressive strength. The blending ratio is 5 to 25 parts by weight, preferably 15 to 20 parts by weight, in terms of anhydride, per 100 parts by weight of alkali bicarbonate. If the amount is less than this range, the gel time will become longer and the strength and durability of the gel will decrease, and if it is more, the gel will become unstable and the strength of the gel will tend to decrease. When using magnesium sulfate, the lower the amount of crystallization water, the better the shelf life of the drug, and it is usually preferable to use pentahydrate or less.
In the present invention, it is essential to use sodium tetrapolyphosphate as an additive having a chelating effect to prevent the formation of a heterogeneous gel, and other alkali phosphate salts and condensed alkali phosphate salts do not achieve the purpose of the present invention. I can't. That is, when primary to tertiary sodium or potassium phosphates are used as an alkali-magnesium bicarbonate gelling agent, precipitation occurs. Also, 5% against alkali bicarbonate.
When a gelling agent containing more than % by weight of a magnesium salt and various alkali condensed phosphate salts are simultaneously dissolved in water, a clear solution is obtained at a practical drug concentration using sodium metaphosphate, sodium trimetaphosphate, sodium trimetaphosphate, and sodium tetrapolyphosphate only, other pyrophosphoric acid, tripolyphosphoric acid, acidic pyrophosphoric acid, hexametaphosphoric acid,
Each of the sodium and potassium salts of acidic hexametaphosphate and pentapolyphosphate, as well as potassium metaphosphate, potassium trimetaphosphate, and potassium tetrapolyphosphate, all cause precipitation. Furthermore, when an aqueous alkali silicate solution is mixed, a good gelled product can be obtained only when sodium tetrapolyphosphate is used as a chelating agent; It was found that even though the solution of the curing agent was transparent, it immediately precipitated to form an unstable gel. The amount of sodium tetrapolyphosphate used in the present invention is 5 to 40 parts by weight per 100 parts by weight of alkali bicarbonate; if it is less than 5 parts by weight, the chelating ability will be insufficient and a good gelled product will not be obtained. If it exceeds 40 parts by weight, precipitation may occur and it is not economical. In the present invention, the following inorganic salts can be used in combination. In other words, alkaline salts such as sodium chloride and potassium chloride,
Although it cannot be a strong gelling agent by itself, it is inexpensive and has good solubility, so it is used as an auxiliary when a shorter gel time is required. When added to an alkali silicate, variations in gel time are reduced even if the mixing ratio with the gelling agent solution varies. Effective inorganic salts when used in combination with a gelling agent containing alkali bicarbonate, magnesium salt, and sodium tetrapolyphosphate as main components include alkali salts selected from sodium chloride, sodium sulfate, potassium sulfate, potassium sulfite, and sodium sulfate. Can be mentioned. Among these, sodium chloride is preferred and may be used in combination with other salts. The preferred amount is 1 to 40 parts by weight per 100 parts by weight of alkali bicarbonate; the larger the amount, the shorter the gel time. Addition of potassium chloride, potassium carbonate, and potassium nitrate alone tends to result in unstable gelation. Inorganic salts that are effective when added to an aqueous alkali silicate solution are alkali salts selected from potassium chloride, sodium chloride, potassium carbonate, potassium sulfite, potassium sulfate, sodium sulfate, and potassium nitrate, and the preferred amount of addition is the aqueous alkali silicate solution. The gel time becomes shorter as the amount increases from 0.1 to 5% by weight based on 100 parts by weight. The component concentration of the gelling agent (b) chemical solution is chemical solution 1.
If the amount is less than 70 g/l, it is difficult to precipitate a strong silicic acid gel, and if it exceeds 200 g/l, the solubility deteriorates and it is economically unsuitable. The soil stabilization work is the same as before; before construction, an alkaline silicate aqueous solution and an aqueous chemical solution of the above composition are prepared separately, pumped through each pipe, mixed at the tip of the pipe, and then pressed into the target ground. do. Aqueous chemical solution of alkaline silicate aqueous solution (a) and gelling agent
The mixing ratio with (b) is generally 3:7 to 7:3, but it can change depending on the condition of the target ground, the construction method adopted, etc. As described above, according to the method of the present invention, an instant setting type grout using alkali bicarbonate as a gelling agent for water glass is produced, the shrinkage is improved with a specific range of magnesium sulfate and chloride, and a specific range of phosphorus is added to the grout. By using sodium tetrapolyphosphate, which is an acid salt chelating agent, in combination, the stability during gelation can be significantly improved throughout the seasons, and the strength in water is also improved. Furthermore, if necessary, inorganic alkali salts can be added to further shorten the gel time. All of the chemicals used in the present invention are inorganic, have no environmental safety concerns, and have great industrial utility value. In the Examples and Comparative Examples shown below, all parts and percentages are based on weight. Examples, Comparative Example 1 Sodium bicarbonate 40g, potassium bicarbonate 40g,
14 g of magnesium sulfate and various alkali phosphates were dissolved in ion-exchanged water to prepare a gelled aqueous solution having a total amount of 1. To 50 ml of the gelling agent aqueous solution from which a transparent solution was obtained, 50 ml of a 23% solids sodium silicate aqueous solution prepared by diluting 25 ml of JIS No. 3 sodium silicate with ion-exchanged water was added. Table 1 shows the results of investigating the situation.

【table】

[Table] Example, Comparative Example 2 10 g of sodium tetrapolyphosphate and alkali bicarbonate, magnesium sulfate, and magnesium chloride were added in various proportions (calculated as anhydride) as shown in Table 2 and dissolved in ion-exchanged water. A gelling agent solution having a total volume of 1 was prepared. Add 50 ml of a 23% solids sodium silicate aqueous solution prepared by diluting 25 ml of JIS No. 3 sodium silicate to 2 times the volume with ion-exchanged water to 50 ml of the gelling agent solution from which a transparent solution was obtained, and raise the liquid temperature to 20°C. The gelation status was investigated. The results are shown in Table 2.

[Table] Alkali bicarbonate 100 gives good results
% of the magnesium salt is 25 parts or less, and the sodium bicarbonate in the alkali bicarbonate is 30% or more. Example 3 50 ml of the same 23% solids sodium silicate aqueous solution as in Examples 1 and 2 and a gelling agent aqueous solution having the composition shown below.
A sand gel was prepared by mixing 100 ml of the mixture and permeating it into compacted Toyoura standard sand to form a gel. Gelation 1
After a period of time, it was completely immersed in water at a constant temperature of 20°C, and the changes in strength over time were measured. The results are shown in Table 3.

【table】

[Table] As shown in Table 3, when no magnesium salt is added, the strength decreases significantly, and when the magnesium salt is added, the strength increases. Example 4, Comparative Example 4 JIS No. 3 sodium silicate 50ml and ion exchange water 50ml
ml to make solution A, 4g of potassium bicarbonate,
4g sodium bicarbonate, 1.2g magnesium sulfate,
Solution B is a solution made by adding ion-exchanged water to 1 g of sodium tetrapolyphosphate to make 100 ml. A liquid,
Various additives were added to each of the B solutions and the AB solutions were mixed, and the gelation state and gel time at 20° C. were measured. The results are shown in Table 4.

[Table] As shown in the table above, potassium chloride is the best additive for liquid A, followed by sodium chloride, potassium carbonate, potassium sulfate, potassium sulfite, sodium sulfate, and potassium nitrate, and the amount of addition is When the amount exceeds 5% of the sodium acid aqueous solution, gelation becomes unstable.
In addition, sodium chloride is the best solution for B,
Next are sodium sulfate, potassium sulfate, potassium sulfite, and sodium nitrate, and if the amount added exceeds 40 parts per 100 parts of alkali bicarbonate, gelation will become unstable. Example 5, Comparative Example 5 Sodium bicarbonate 40g, potassium bicarbonate 40g,
A solution called 1 was prepared by dissolving 8 g of magnesium sulfate (calculated as anhydride) and 10 g of sodium tetrapolyphosphate in ion-exchanged water, and a solution called 1 was prepared by omitting only the sodium tetrapolyphosphate. On the other hand, ion-exchanged water was added to 500 ml of JIS No. 3 sodium silicate to prepare an aqueous alkali silicate solution. The gelling agent aqueous solution and the sodium silicate aqueous solution were each taken in equal volumes and mixed at a liquid temperature of 20° C. and 30° C., respectively, and the gelling state and gel time were measured. The results are shown in Table 5.

[Table] In other words, when using an aqueous gelling agent solution containing sodium tetrapolyphosphate, the gelation state was good at both 20°C and 33°C, and the gel time was stable in each case. When an aqueous gelling agent solution containing no sodium phosphate was used, partial gelation occurred at 33°C, resulting in a non-uniform gel.

Claims (1)

[Scope of Claims] 1 (a) an aqueous alkali silicate solution with a solid content of 10 to 40% by weight, (b) 30 to 100% of sodium bicarbonate as a gelling agent.
per 100 parts by weight of alkali bicarbonate consisting of 0 to 70% by weight of potassium bicarbonate, 5 to 25 parts by weight of magnesium sulfate or chloride alone or as a mixture (calculated as anhydride), and 5 parts by weight of sodium tetrapolyphosphate. Concentrations 70-200 containing ~40 parts by weight
A ground improvement method characterized by injecting the above (a) and (b) into the ground and curing it. 2 (a) an aqueous alkali silicate solution with a solid content of 10 to 40% by weight, (b) 30 to 100% of sodium bicarbonate as a gelling agent.
per 100 parts by weight of alkali bicarbonate consisting of 0 to 70% by weight of potassium bicarbonate, 5 to 25 parts by weight of magnesium sulfate or chloride alone or as a mixture (calculated as anhydride), and 5 parts by weight of sodium tetrapolyphosphate. Concentrations 70-200 containing ~40 parts by weight
When injecting (a) and (b) above into the ground and curing it, add potassium chloride, sodium chloride, potassium carbonate, potassium sulfite, potassium sulfate, sodium sulfate, or potassium nitrate to solution (a) in advance. Kao (a) liquid
Add 0.1 to 5 parts by weight per 100 parts by weight, and/or add sodium chloride, sodium sulfate,
1. A method for ground improvement, which comprises adding 1 to 40 parts by weight of potassium sulfate, potassium sulfite, or sodium nitrate to 100 parts by weight of alkali bicarbonate in solution (b).