Method for constructing impervious wall

Abstract

To provide a construction method of an impervious wall capable of shortening a construction time.SOLUTION: The aqueous solution and the powdery bentonite are supplied to the ground by 1.5 shots or 2 shots, the aqueous solution contains an alkali metal salt or the like which is a swelling inhibitor, the aqueous solution necessary for the construction of the impervious wall is supplied to the ground first, the powdery bentonite is supplied next, and a thickener and additional powdery bentonite can be further added as needed.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for constructing a water barrier wall. [Background technology]

[0002] Underground impermeable walls have been constructed to prevent water leakage from embankments, contain contaminated soil, etc. Conventional methods for constructing impermeable walls have involved the construction of underground impermeable walls using slurry with cement-based solidification materials, cement-bentonite slurry, bentonite, etc.

[0003] However, when constructing a watertight wall using conventional methods, it is difficult to adjust the required amounts of cement-based solidification material, cement-bentonite slurry, bentonite, etc., which results in unstable quality of the watertight wall. Furthermore, there are environmental issues, such as the large amount of water required to mix the slurry underground and the large amount of soil discharged during excavation. Therefore, a method was developed that stabilizes the quality of underground watertight walls and reduces the environmental impact of their construction.

[0004] One method of constructing such a water impermeable wall is disclosed in which ground soil is excavated underground with muddy water, and then cement milk containing a solidifying agent containing bicarbonate is injected and mixed with the ground soil underground to solidify it (Patent Document 1). This method makes it easy to adjust the required amount of bicarbonate contained in the solidifying agent, thereby stabilizing the quality of the underground water impermeable wall. Furthermore, because the cement milk, solidifying agent, and ground soil are mixed and stirred underground, the amount of soil discharged can be reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2021-46685 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned method for constructing a water barrier requires first excavating muddy water underground and then pouring in cement milk containing a solidifying agent, which can result in a problem of long construction times.

[0007] Therefore, an object of the present invention is to provide a method for constructing a water impermeable wall that can shorten the construction time. [Means for solving the problem]

[0008] The present invention, which has solved the above problems, is as follows. [First aspect] The aqueous solution and powdered bentonite are supplied to the ground in 1.5 or 2 shots. The aqueous solution contains a swelling inhibitor and is supplied prior to the powdered bentonite. A method for constructing a watertight wall.

[0009] [Second Aspect] The concentration of bentonite in the supply of the aqueous solution and the powdered bentonite is 100 to 2000 g / L. A method for constructing a watertight wall according to a first aspect.

[0010] [Third Aspect] The supply of the powdered bentonite is carried out together with the supply of the thickener; A method for constructing a watertight wall according to a first aspect. [Effects of the Invention]

[0011] According to the present invention, a method for constructing a water impermeable wall can be achieved that can shorten construction time. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, an embodiment of the present invention will be described. Note that this embodiment is an example of the present invention. The scope of the present invention is not limited to the scope of this embodiment.

[0013] In the method for constructing a water impermeable wall of this embodiment, powdered bentonite is supplied to an aqueous solution containing a swelling inhibitor immediately before the aqueous solution is supplied to the ground, thereby constructing the water impermeable wall. Note that, in this specification, bentonite refers to a clay mineral containing montmorillonite as a main component.

[0014] (First form) In the method for constructing a water impermeable wall of this embodiment, an aqueous solution containing a swelling inhibitor is supplied, and immediately thereafter, bentonite powder is supplied. "Immediately thereafter" refers to the period after the start of discharging the aqueous solution, for example, from immediately after discharging to 5 minutes after discharging. Alternatively, bentonite powder may be supplied to the aqueous solution immediately before discharging the bentonite muddy water into the ground. "Immediately thereafter" refers to the point in the line leading from the plant to the ground just before it reaches the ground. If the supply order is reversed, with bentonite powder supplied first and then the aqueous solution containing a swelling inhibitor, the bentonite powder will clump and become poorly dispersible.

[0015] Because the aqueous solution and powdered bentonite are delivered to the ground in 1.5 or 2 shots, the viscosity of the solution and powdered bentonite is higher than with a 1-shot delivery, and even though the swelling suppression is lower when the solution and powdered bentonite are mixed, it is possible to mix them in the line or in the ground. This method not only allows more powdered bentonite to be delivered to the ground than with a 1-shot delivery, but also reduces the amount of liquid delivered, which reduces the amount of water delivered to the ground and allows for the creation of a harder wall. Furthermore, because the swelling suppression is low, it is possible to reduce the amount of swelling suppressants, such as alkali metal salts.

[0016] Incidentally, the upper limit of the bentonite concentration that can be used to prepare bentonite mud for one shot is 70%. For 1.5 shots and 2 shots, there is no need to prepare the bentonite mud in advance, and the mud is prepared just before or within the ground, so it is possible to further increase the bentonite concentration of the bentonite mud.

[0017] Conventionally, when constructing a water barrier, the aqueous solution is uniformly supplied to the ground in accordance with the moving speed of the cutter post that is generally used. However, in this embodiment, when using the cutter post, the aqueous solution is first discharged, followed by the powdered bentonite. If this order is not followed, the powdered bentonite will not disperse, making construction difficult. For example, if the cutter post is 1m long, 3 The total amount of aqueous solution required to construct the impermeable wall is 30 L to 250 L, preferably 50 L to 200 L. The amount of aqueous solution discharged in advance is 1% to 100%, preferably 10% to 50%, of the total amount of aqueous solution required to construct the impermeable wall. If the amount of aqueous solution discharged in advance is less than 1%, the water content is low, and the dispersibility of the powder added later is likely to be poor. The proportion of aqueous solution discharged in advance out of the total amount of aqueous solution required to construct the impermeable wall varies depending on the construction method. For example, in the pile construction method, 100% of the aqueous solution is discharged in advance. In other construction methods, such as wall formation, if the amount of aqueous solution discharged in advance is more than 50%, even if the remaining aqueous solution is mixed with powdered bentonite and added later, the viscosity does not increase, making the impermeable wall difficult to solidify, and the impermeable wall's water resistance and strength are likely to be reduced. If the viscosity does not increase, it is possible to increase the viscosity by supplying more powdered bentonite than planned.

[0018] The concentration of powdered bentonite supplied to the ground is 100 to 2000 g / L, preferably 300 to 1200 g / L, in the combined supply of aqueous solution and powdered bentonite. If the concentration of powdered bentonite in the supply is less than 100 g / L, there will not be enough bentonite, resulting in low impermeability and strength of the water impermeable wall. If the concentration of powdered bentonite in the supply is more than 2000 g / L, the powdered bentonite will not disperse uniformly, resulting in clumps, making workability difficult.

[0019] To facilitate the construction of the water barrier, a thickener can be added to the ground as needed. Thickeners can be added to the swelling inhibitor, but the amount added is limited because it may increase the viscosity of the aqueous solution and make it difficult to pump. Alternatively, they can be added as a powder together with powdered bentonite. In this case, there is no limit to the amount added to the swelling inhibitor, and it varies depending on the ground conditions, construction area, and amount of powdered bentonite. For example, 0.1 kg to 5 kg, preferably 0.2 kg to 1 kg, of various thickeners can be added to 100 L of bentonite mud water. There are no restrictions on the type of thickener that can be added; any common powder thickener will do.

[0020] In the case of 1 shot, adding a thickener would increase the viscosity of the bentonite mud, making it difficult to transport through the line, so adding a thickener was not suitable. In the case of 1.5 shot, even if the viscosity of the bentonite mud increases, the mud can still be transported as long as the pipe after the aqueous solution and powdered bentonite join is short, so adding a thickener is possible. In the case of 2 shot, the aqueous solution and powdered bentonite are mixed inside the ground, so there is no effect on transport, and a thickener can be added.

[0021] (aqueous solution) The aqueous solution is a solution in which the swelling inhibitor is mixed with water. Other substances may be contained within the range that does not impair the present invention.

[0022] The swelling inhibitor contained in the aqueous solution is not limited as long as it can inhibit the swelling of bentonite. For example, alkali metal salts are preferable, and among them, inorganic acid salts and organic acid salts, which are electrolytes, are preferable. Carbonates, phosphates, silicates, sulfates, chlorides, etc. can also be used as highly versatile agents.

[0023] The concentration of the swelling inhibitor in the aqueous solution must be 5% or higher, with no upper limit. For example, a concentration up to the point where the swelling inhibitor can be dissolved is preferable, and this concentration varies depending on the amount of bentonite and water content supplied. For example, for 1.5 shots, a high concentration of swelling inhibitor is required, while for 2 shots, a lower concentration is acceptable. If the concentration of the swelling inhibitor is less than 5%, it will not function properly as a swelling inhibitor. The powdered bentonite will swell, resulting in poor dispersibility. [Example]

[0024] Example 1 Aqueous solution (A) and 50g of powdered bentonite (B) were added to moist sand, simulating saturated sandy ground, in 1 shot, 1.5 shots, and 2 shots, respectively, and then 10g of powdered bentonite was added and mixed. Using this sample soil, an indoor permeability test was conducted and the mixing status with the sandy ground was confirmed. In Test Examples 1 and 2, the content of sodium carbonate, a swelling inhibitor in the aqueous solution (A), was set to 4.5g and 3g, respectively, and the concentration of sodium carbonate was changed.

[0025] In both Test Examples 1 and 2, for one shot, aqueous solution (A) and powdered bentonite (B) were mixed to prepare bentonite mud, simulating the preparation time and kneading time at the actual site, and the slurry was poured into the sandy ground 30 minutes later. For 1.5 shots, aqueous solution (A) and powdered bentonite (B) were placed in separate cups, and the aqueous solution (A) and powdered bentonite (B) were poured into the sandy ground immediately after mixing. For two shots, aqueous solution (A) and powdered bentonite (B) were placed in separate cups and poured into the sandy ground at the same time. [Table 1]

[0026] Regarding mixing with sand, the results of Test Example 2 showed that in the case of 1 shot, if the concentration of sodium carbonate in the aqueous solution (A) was low, the swelling of the powdered bentonite (B) was not suppressed, the bentonite mud became highly viscous, and it was difficult to inject into the ground. On the other hand, in the case of 1.5 shots, the specified amounts of aqueous solution (A) and powdered bentonite (B) were mixed in a short time, and the bentonite mud could be injected into the ground immediately after mixing. Therefore, even if the sodium carbonate concentration was low, the viscosity did not increase, and no problems occurred with mixing in either Test Example 1 or Test Example 2. In the case of 2 shots, the specified amounts of aqueous solution (A) and powdered bentonite (B) were mixed within the sandy ground, so no problems occurred with mixing.

[0027] In the permeability tests, the permeability coefficients for 1.5 shots and 2 shots were smaller than the impermeable coefficient for 1 shot in both Test Example 1 and Test Example 2. This shows that the impermeable walls constructed with 1.5 shots and 2 shots have better impermeability than the impermeable wall constructed with 1 shot.

[0028] In the case of 1.5 shots, even though the mixing of the powdered bentonite supplied after the bentonite mud solution is less than in the case of 1 shot, the sodium carbonate prevents the powdered bentonite from swelling, and the hydraulic conductivity indicates that the powdered bentonite is dispersed in the ground by mechanical mixing. In the case of 2 shots, bentonite mud is prepared in the ground, but as in the case of 1.5 shots, the sodium carbonate prevents the powdered bentonite from swelling, and the hydraulic conductivity indicates that the powdered bentonite is easily dispersed in the ground by mechanical mixing. [Industrial Applicability]

[0029] The present invention can be used as a method for constructing a water impermeable wall.

Claims

1. The aqueous solution and powdered bentonite are supplied to the ground in 1.5 shots or 2 shots. The aqueous solution contains a swelling inhibitor and is supplied prior to the powdered bentonite. A method for constructing a watertight wall.

2. The bentonite concentration in the supply of the aqueous solution and the powdered bentonite is 100 to 2000 g / L; A method for constructing a water barrier wall according to claim 1.

3. The supply of the powdered bentonite is carried out together with the supply of the thickener; A method for constructing a water barrier wall according to claim 1.

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