JP7128731B2 - Construction method of impermeable wall - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for constructing impermeable walls.

As a method for constructing impermeable walls, for example, there is a method disclosed in Patent Document 1. In the method disclosed in the document, muddy water such as Ca-type bentonite is supplied into the ground and mixed, and a liquid of an ion exchange agent that reforms the Ca-type bentonite or the like into Na-type bentonite or the like is supplied into the ground. It is a mixture. This document states that there is a problem in homogeneous mixing when bentonite powder is added, and that Ca-type bentonite and the like and an ion exchange agent are supplied in the form of a liquid.

However, according to this method, a large amount of water is injected into the ground, and it is thought that the impermeable wall will become soft.

Japanese Patent No. 6163173

The main problem to be solved by the present invention is to provide a method for constructing a water impermeable wall that can construct a water impermeable wall having sufficient strength without causing a problem in mixing the bentonite with the ground. .

Means for solving the above problems are as follows.
(Means according to claim 1)
A method for constructing a water impermeable wall in which bentonite is supplied to the ground and stirred,
supplying a bentonite liquid having exchangeable cations to the ground;
then supplying powder of alkaline earth metal bentonite and powder of ion exchange agent to the ground;
A method for constructing an impermeable wall characterized by:

(Means according to claim 2)
The bentonite liquid having the exchangeable cation is an alkaline earth metal bentonite liquid,
The alkaline earth metal bentonite liquid has a concentration of 5 to 60 W/V%.
The construction method of the impermeable wall according to claim 1.

(Means according to claim 3)
The amount of the alkaline earth metal bentonite liquid supplied per 1 m ³ of the ground is 50 to 200 L,
The amount of the alkaline earth metal bentonite powder supplied is such that the total amount of bentonite supplied per 1 m ³ of the ground is 50 to 300 kg.
The construction method of the impermeable wall according to claim 2.

(Means according to claim 4)
The ion exchange agent is sodium carbonate,
The amount of the ion exchange agent supplied to 1 kg of the alkaline earth metal bentonite is 0.01 to 0.2 kg.
The construction method of the impermeable wall according to claim 2 or 3.

According to the present invention, there is provided a method for constructing impermeable walls that can construct impermeable walls having sufficient strength without causing problems in the mixing of bentonite and ground.

It is explanatory drawing which shows the procedure of the construction method of an impervious wall.

Next, the form for implementing this invention is demonstrated. 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.

As shown in FIG. 1, in the impermeable wall construction method of the present embodiment, first, liquid BW of bentonite having exchangeable cations, which are interlayer cations, is supplied (injected) into the ground G (preceding process 100). . Next, alkaline earth metal bentonite powder CP having alkaline earth metal ions that are multivalent cations as interlayer cations and ion exchanger powder IP are supplied (thrown in) to the ground G (after row processing 200).

Then, the ground G is stirred at an appropriate stage to mix the bentonite or the like with the ground G. This mixing can be done in the process (100, 200) of feeding liquid BW or powder CP, IP, or before or after this process (100, 200). Specifically, for example, it can be performed after the preceding process 100 and the succeeding process 200, or only after the succeeding process 200, or in the middle (process) of the preceding process 100 or the succeeding process 200.

In the present embodiment, bentonite means clay containing montmorillonite as a main component. Interlayer cations mean ions existing between layers of montmorillonite. Interlayer cations include, for example, monovalent cations such as sodium ions and lithium ions, and divalent or trivalent cations such as calcium ions and magnesium ions. In the following description, various bentonites containing a large amount of alkali metal ions such as sodium ions as interlayer cations are referred to as "Na-type bentonite" or "alkali metal-type bentonite". In addition, a case in which a large amount of alkaline earth metal ions such as calcium ions and magnesium ions are contained as interlayer cations is called "Ca type bentonite" or "alkaline earth metal type bentonite".

Na-type bentonite is excellent in swelling properties and thickening properties. Therefore, it is suitable for constructing impermeable walls. However, when Na-type bentonite is turned into muddy water (liquid), it is difficult to increase the concentration. On the other hand, Ca-type bentonite is inferior in swelling properties and thickening properties. Therefore, it is unsuitable for constructing impermeable walls. However, in the case of making muddy water (liquid), it has the advantage that it is easy to increase the concentration.

On the other hand, the interlayer cations of montmorillonite are exchangeable cations, which are easy to ion-exchange with other cations. Therefore, one of the features of the present embodiment is that an ion exchange agent is used to take advantage of both the characteristics of Na-type bentonite and Ca-type bentonite. Therefore, in the present embodiment, the ion exchange agent means an agent capable of modifying (ion-exchanging) Ca-type bentonite into Na-type bentonite.

Na-type bentonite obtained by ion exchange (modification) of Ca-type bentonite is also referred to as modified Na-type bentonite or activated Na-type bentonite. Further, the reaction formula when ion exchange is performed using sodium carbonate is as follows.
Be--Ca + Na ₂ CO ₃ →Be--Na + CaCO ₃

Bentonite liquid BW with exchangeable cations can be widely used in the pretreatment 100 . However, as the liquid BW of bentonite having exchangeable cations, it is preferable to use a liquid of Ca-type bentonite. As described above, the Ca-type bentonite can be made highly concentrated and can reduce the injection of moisture into the ground G. Reducing water injection reduces the amount of sludge discharged and increases the strength of the impermeable wall. Furthermore, a high concentration improves the dispersibility of bentonite.

When a Ca-bentonite liquid is used, the concentration of the liquid is preferably 1 to 80 W/V%, more preferably 3 to 70 W/V%, and particularly preferably 5 to 60 W/V%. If the concentration is less than 1 W/V%, the liquid BW of bentonite may have insufficient wall building properties (for example, the ability to prevent the ground G from collapsing). On the other hand, if the concentration exceeds 80 W/V %, it may be difficult to prepare the solution.

The liquid concentration of Ca-type bentonite means the proportion (%) of the mass (kg) of bentonite per 1 m ³ of slurry (mud) working solution water (external ratio). Therefore, for example, 5 to 60 W/V% means 50 to 600 kg/m ³ .

In the subsequent treatment 200, Ca-bentonite powder CP is used. Ca-type bentonite is inferior in swelling property, thickening property, etc., but it is easy to mix with the ground G even if it is a powder. This is because the Ca-bentonite powder has a lower water absorption and swelling property than the Na-bentonite powder, so even if it is added to and mixed with water, it will not form lumps and will be uniformly dispersed. It is for In addition, by supplying Ca-type bentonite in the post-treatment 200, the supply of bentonite in the pre-treatment 100 can be reduced. Furthermore, since the amount of water to be supplied (injected) into the ground G is reduced when the powder is used, the strength of the resulting impermeable wall is improved. In other words, if it is powder, there is an advantage that the water impermeable wall can be made hard, and while the required amount of bentonite is supplied to the ground G, sludge discharge can be reduced.

However, from the viewpoint of reducing the moisture supplied to the ground G, it is preferable to use a high-concentration Ca-bentonite liquid in the preceding treatment 100. It is more preferable to use .

First, in the preliminary treatment 100, the injection amount of Ca-bentonite liquid BW (concentration 5 to 60 W/V%) per ground G (1 m ³ ) varies depending on the soil quality of the target ground, but is preferably 10 to 400 L, More preferably 20-300L, particularly preferably 50-200L.

On the other hand, in the subsequent treatment 200, the amount of Ca-type bentonite powder CP charged is preferably the total amount of bentonite supplied per ground G (1 m ³ ) (in the present embodiment, bentonite liquid BW and bentonite The total amount of the powder CP is 50 to 300 kg.

In some cases, Na-type bentonite mud water reaches its limit for pumping at a concentration of around 10%, but Ca-type bentonite mud water can be pumped even at a high concentration of 50 to 60%. Therefore, if a high-concentration Ca-bentonite mud is used, a large amount of bentonite can be supplied to the ground G with the same amount of injection, and the subsequent supply amount of bentonite powder can be reduced accordingly. For example, as is clear from the examples below, when construction is performed so that the total amount of bentonite in the ground G is 100 kg, the amount of Ca-type bentonite powder supplied after 100 L of mud water with a concentration (5%) is 95 kg ( Table 1), the supply amount of Ca-bentonite powder after 100 L of concentrated (50%) muddy water is injected is 58 kg (see Table 2), which can be reduced by about 40%.

In this embodiment, as the ion exchange agent, general agents capable of modifying (ion-exchanging) Ca-type bentonite into Na-type bentonite can be used. Specifically, for example, ion exchangers made of sodium carbonate, sodium hydrogencarbonate, sodium percarbonate, sodium hydroxide, sodium citrate, sodium silicate, etc., phosphoric acid-based ion-exchangers, silica-based ion-exchangers 1 type or 2 or more types can be selected and used from among. However, it is preferable to use an ion exchange agent that ion-exchanges alkali metal ions such as sodium ions and alkaline earth metal ions such as calcium ions, and insolubilizes or chelates the precipitated alkaline earth metal ions to precipitate them. As such an ion exchange agent, for example, it is preferable to use an ion exchange agent such as a sulfuric acid salt, a phosphoric acid salt, a silicic acid salt, an ethylenediamine salt, a carboxylic acid salt, and sodium carbonate is preferably used. is more preferred.

The amount of ion exchange agent added is preferably 0.01 to 0.2 kg, more preferably 0.02 to 0.15 kg, and particularly preferably 0.03 to 0.1 kg, relative to Ca-type bentonite (1 kg). be. If the input amount is less than 0.01 kg, the Ca-bentonite may not be sufficiently reformed. On the other hand, if the input amount exceeds 0.2 kg, the ion exchange agent may become excessive.

The ion exchange agent powder IP may be supplied to the ground G separately from the Ca-bentonite powder CP, or may be supplied to the ground G after being mixed.

(others)
In the method of this embodiment, for example, a water impermeable wall using a "chain cutter type excavator equipped with a movable base machine and a cutter for excavating a groove in the ground" as disclosed in Japanese Patent Application Laid-Open No. 2005-16295. (Equal-thickness type), or when constructing an impermeable wall using a "drilling rig equipped with a single-axis or multi-axis drilling axis" as disclosed in Japanese Patent Application Laid-Open No. 2006-291703 ( column type), and can be applied when constructing a water impermeable wall using a backhoe equipped with a bucket.

Next, examples of the present invention will be described.
(Test 1)
In this test, first, bentonite mud was added to sand (A) and mixed (first mixing). As the bentonite mud, a low-concentration (5%) Ca-bentonite liquid (mud) or an activated Ca-bentonite liquid (mud) was used. Next, Ca-bentonite powder and soda ash (sodium carbonate) powder were added to the sand after the first mixing and mixed (second mixing). Table 1 shows the table flow values after the first mixing and after the second mixing, and the hydraulic conductivity. The following standards exist for the hydraulic conductivity.
Environmental site conditions: 1×10 ^-8 m/sec or less Civil engineering site conditions: 1×10 ^-6 m/sec or less

The table flow value is an index of fluidity, and corresponds to the time of excavation at the time of first mixing, and corresponds to the time of preparation at the time of second mixing. For example, if the table flow value at the time of construction is 130 or less, there is almost no fluidization, and if the prescribed amount of bentonite is added, it will have a hardness that does not pose a problem in terms of waterproofing for environmental sites. .

(Test 2)
In this test, first, bentonite mud and soda ash were added to sand (A) and mixed (first mixing). As the bentonite mud, a liquid (mud) of high-concentration (50%) Ca-type bentonite was used. Next, nothing was added to the sand after the first mixing, or Ca-bentonite powder and soda ash powder were added and mixed (second mixing). Table 2 shows the table flow values after the first mixing and after the second mixing, and the hydraulic conductivity.

From Table 2, it can be seen that it is preferable to add not only soda ash but also Ca-bentonite powder.

(Test 3)
In this test, first, bentonite mud, Ca-type bentonite powder, and soda ash powder were added to sand (A) and mixed (first mixing). As the bentonite mud, a Ca-type bentonite liquid (mud) was used. Next, Ca-bentonite powder and soda ash powder were added to the sand after the first mixing and mixed (second mixing). Table 3 shows the table flow values after the first mixing and after the second mixing, and the hydraulic conductivity. Furthermore, similar tests were conducted using Ca-type bentonite (B) from different production areas (Test Examples 15 and 16).

From Table 3, it can be seen that by adding the Ca-bentonite powder together with the muddy water during the first mixing, it is possible to adjust the fluidity to an appropriate level.

INDUSTRIAL APPLICABILITY The present invention can be used as a method for constructing impermeable walls.

100 Preceding treatment 200 Succeeding treatment BW Bentonite mud CP Ca-type bentonite powder IP Ion exchanger powder G Ground

Claims (4)

A method for constructing a water impermeable wall in which bentonite is supplied to the ground and stirred,
supplying a bentonite liquid having exchangeable cations to the ground;
then supplying powder of alkaline earth metal bentonite and powder of ion exchange agent to the ground;
A method for constructing an impermeable wall characterized by: The bentonite liquid having the exchangeable cation is an alkaline earth metal bentonite liquid,
The alkaline earth metal bentonite liquid has a concentration of 5 to 60 W/V%.
The construction method of the impermeable wall according to claim 1. The amount of the alkaline earth metal bentonite liquid supplied per 1 m ³ of the ground is 50 to 200 L,
The amount of the alkaline earth metal bentonite powder supplied is such that the total amount of bentonite supplied per 1 m ³ of the ground is 50 to 300 kg.
The construction method of the impermeable wall according to claim 2. The ion exchange agent is sodium carbonate,
The amount of the ion exchange agent supplied to 1 kg of the alkaline earth metal bentonite is 0.01 to 0.2 kg.
The construction method of the impermeable wall according to claim 2 or 3.

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