Method for constructing impervious wall

Abstract

To provide a construction method of an impervious wall capable of shortening a construction time.SOLUTION: When muddy water containing bentonite is supplied to the ground, powdery bentonite is supplied, and alkali metal salt contained in the muddy water acts on the bentonite.SELECTED DRAWING: Figure 1

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] When supplying muddy water containing bentonite to the ground, powdered bentonite is supplied, The muddy water contains an alkali metal salt. A method for constructing a watertight wall.

[0009] [Second Aspect] A carbonate is used as the alkali metal salt. A method for constructing a watertight wall according to a first aspect.

[0010] [Third Aspect] Ca-type bentonite is used as at least one of the bentonite contained in the muddy water and the powdered bentonite. A method for constructing a watertight wall according to the first or second aspect.

[0011] [Fourth aspect] The amount of the powdered bentonite is 80% or less of the total amount of bentonite to be supplied to the ground. A method for constructing a watertight wall according to the first or second aspect. [Effects of the Invention]

[0012] According to the present invention, a method for constructing a water impermeable wall can be achieved that can shorten construction time. [Brief explanation of the drawings]

[0013] [Figure 1]These are the results of measuring the hydraulic conductivity of a water-impermeable wall material created by simultaneously adding bentonite powder to high-concentration bentonite mud water. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] In the method for constructing a water impermeable wall of this embodiment, bentonite mud is supplied to the ground, and at the same time, powdered bentonite is supplied to the ground. The bentonite mud is prepared by adding bentonite to water containing an alkali metal salt. It is desirable to use at least one of Na-type bentonite and Ca-type bentonite as the bentonite.

[0016] (First form) In the method for constructing a water impermeable wall of this embodiment, when bentonite mud is supplied to the ground, bentonite powder is also supplied to the ground. The concentration of the bentonite mud is 10% to 80%. The amount of alkali metal salt added to the bentonite mud is, for example, 12% to 25% for Na-type bentonite and 5% to 22% for Ca-type bentonite, relative to the total amount of bentonite supplied to the ground, to prepare the bentonite mud. In this specification, bentonite refers to a clay mineral whose main component is montmorillonite.

[0017] In the past, when bentonite mud solution with a concentration of approximately 5 to 10% was supplied to the ground and bentonite powder was also supplied, the bentonite rapidly swelled and became less dispersible, making it difficult to construct a waterproof wall. In this method, the bentonite mud solution has a relatively high concentration, and the alkali metal salts present in the bentonite mud inhibit the swelling of the bentonite, improving dispersibility and making it easier to construct a waterproof wall. Furthermore, because the bentonite mud solution has a relatively high concentration, the water content is kept low, resulting in a waterproof wall that has high waterproofing performance and hardness.

[0018] The alkali metal salts in the bentonite mud are preferably inorganic or organic acid salts, which are electrolytes. Examples of widely used salts include carbonates, phosphates, silicates, sulfates, and chlorides. However, carbonates, phosphates, and silicates are preferred as alkali metal salts. The use of these alkali metal salts is inexpensive and can ion-exchange some of the exchangeable alkaline earth metal ions contained in the sodium-type bentonite, thereby increasing the swelling capacity. Furthermore, if polyvalent metal ions, which are swelling inhibitors, are present in the groundwater, these substances are insolubilized.

[0019] The alkali metal salts in the bentonite mud work to suppress the swelling of powdered bentonite, especially sodium bentonite. For example, carbonates are more economical to use than other alkali metal salts. This allows for good dispersibility and workability when the bentonite mud and powdered bentonite are poured into the ground.

[0020] As the powdered bentonite absorbs the water in the mud, the concentration of sodium bentonite in the ground increases, accelerating the swelling of the bentonite in the bentonite mud, and increasing the impermeability and strength of the impermeable wall.

[0021] In the case of Ca-type bentonite, it was found that the powdered bentonite swells due to the alkali metal salts in the mud, and then the swelling is suppressed by the alkali metal salts in the bentonite mud. This means that even if the powdered bentonite is added together with the bentonite mud, it has good activation and workability. Ca-type bentonite is less likely to swell suddenly, so it is less likely to form lumps and has good dispersibility. The powdered bentonite absorbs the water in the mud, hardening the impermeable wall.

[0022] Ca-type bentonite is unsuitable for constructing impermeable walls because it has poor swelling and viscosity properties. Therefore, when using Ca-type bentonite, it is preferable to use an alkali metal salt that functions as an ion exchanger. The Ca-type bentonite is modified (ion exchanged) to Na-type bentonite using an ion exchanger. To activate the Ca-type bentonite, carbonates in the mud react and are consumed. This reduces the concentration of carbonates in the mud, which accelerates the swelling of the bentonite in the mud. As a result, the impermeable wall has higher water resistance and strength than construction using mud alone.

[0023] The amount of powdered bentonite supplied together with the bentonite-containing muddy water is 1% to 99% of the total amount of bentonite supplied to the ground, more preferably 10% to 80%, and even more preferably 10% to 30%. If the amount of powder is more than 80%, the amount of moisture relative to the powder may be insufficient, making it difficult to supply to the ground. If the amount of powder is 80% or less, the powder will be more dispersible and easier to supply to the ground. If the amount of powder is less than 1%, the moisture ratio will be high and the bentonite concentration will decrease, resulting in a weaker water barrier.

[0024] (others) In the above-mentioned method for constructing a watertight wall, bentonite of 100 to 300 mesh, for example, can be used. There is no limitation on the actual equipment, but for example, a "chain cutter type excavation device equipped with a movable base machine and a cutter for excavating a trench in the ground" (equal thickness type) or an "excavation device equipped with single or multiple excavation axes" (column type) can be used. [Example]

[0025] (Experimental Example 1) In order to confirm the dispersibility and swelling properties of bentonite, as well as the hardness of the impermeable wall when powdered bentonite is added to muddy water containing bentonite, an experiment was conducted using a bench mixer to reproduce the soil conditions that occur when muddy water and powder are mixed in saturated ground.

[0026] To compare the dispersibility of powdered bentonite, a 500 ml cup (bottom diameter 80 mm, top diameter 100 mm) was filled with 350 g of sand and 70 ml of water to create a saturated ground state. 10 to 40 ml of bentonite mud (5% mud, high concentration mud) was then added to the sand, creating a mud-mixed ground with a uniformly mixed ground volume of 200 ml.

[0027] A stirring blade (a four-blade downward-pressing blade with a diameter of 65 mm) was pushed into the sand, and 10 g of bentonite powder was added while stirring at 200 rpm. [Table 1]

[0028] In the case of the sand layer mixed with high-concentration bentonite mud water in Test Examples 1 to 3, the bentonite powder added later was easily dispersed, and no clumps of powder were observed adhering to the blade. Furthermore, when the sample soil was beaten after mixing, water did not float up. This is thought to be because the powdered bentonite was uniformly dispersed in the sand, and the amount of bentonite was greater than the salt content in the high-concentration bentonite mud water, which accelerated swelling of the powdered bentonite, preventing water from floating up even when beaten after mixing. When the amount of added mud water was the same, the sand layer mixed with high-concentration bentonite mud water had a higher shear strength than the sand layer mixed with 5% bentonite mud water. For example, Test Example 1 had a shear strength of 4.95 kN / m 2 and 2.93 kN / m in Test Example 4 2 Similarly, Test Example 2 has a higher shear strength than Test Example 4, and Test Example 3 has a higher shear strength than Test Example 6, indicating that high-concentration bentonite mud specifications tend to result in the construction of hard and strong impermeable walls.

[0029] In the case of the sand layer mixed with 5% bentonite mud water in Test Examples 3 to 5, clumps of bentonite powder tended to adhere to the blade, and many undispersed bentonite powders were found. Furthermore, when the mixed sample soil was struck, water floated up. This is thought to be because the bentonite powder was difficult to disperse, was not uniformly dispersed among the soil particles, and required time for swelling, causing water to float up when the sample soil was struck after mixing. The shear strength indicates that the use of 5% bentonite mud water tends to prevent the impermeable wall from becoming hard.

[0030] From the above, it can be considered that when supplying high-concentration bentonite mud to the ground, supplying bentonite powder as well results in less adhesion of the bentonite powder to machinery than supplying bentonite powder to 5% bentonite mud, and accelerates the swelling of the bentonite powder supplied in the bentonite mud, resulting in the creation of a hard and strong impermeable wall.

[0031] Incidentally, it is believed that the ground density of the sand layer into which bentonite mud water is mixed decreases due to stirring. In Test Example 1 or Test Example 4, the moisture content in the ground was below the pore volume, so the amount of moisture contained in the ground was low, and it is believed that the shear strength was high. In Test Example 2 or Test Example 4, the moisture content in the ground was above the pore volume, so the amount of moisture contained in the ground was high, and it is believed that the shear strength was lower than in Test Example 1 or Test Example 4. In Test Examples 1 to 3 or Test Examples 4 to 6, the shear strength decreased as the amount of bentonite mud water added increased. This is believed to be due to the fact that the soil particles were dispersed in the mud water when the amount of liquid added to the ground increased, causing greater slippage.

[0032] (Experimental Example 2) Figure 1 shows the results of measuring the hydraulic conductivity of a water-impermeable wall material created by simultaneously adding bentonite powder to high-concentration bentonite muddy water.

[0033] Compared to a water barrier wall with 5% bentonite slurry containing the same amount of powdered bentonite, a water barrier wall with a high concentration of bentonite slurry has a smaller hydraulic conductivity, indicating superior water barrier performance. Based on these results, it is believed that adding bentonite powder at the same time as using high concentration bentonite slurry is effective. [Industrial Applicability]

[0034] The present invention can be used as a method for constructing a water barrier wall.

Claims

1. When supplying muddy water containing bentonite to the ground, powdered bentonite is supplied, The muddy water contains an alkali metal salt. A method for constructing a watertight wall.

2. A carbonate is used as the alkali metal salt. A method for constructing a water impermeable wall according to claim 1.

3. Ca-type bentonite is used as at least one of the bentonite contained in the muddy water and the powdered bentonite. A method for constructing a water impermeable wall according to claim 1 or 2.

4. The amount of the powdered bentonite is 80% or less of the total amount of bentonite to be supplied to the ground. A method for constructing a water impermeable wall according to claim 1 or 2.

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