JPH0473490B2 - - Google Patents

Description

[Detailed Description of the Invention] <<Industrial Application Field>> The present invention relates to a method of constructing a water-shielding wall, and in particular,
This invention relates to a construction method that improves the water-shielding performance of water-shielding walls.

<<Prior Art>> As is well known, methods for constructing impermeable walls include, for example, the sheet pile wall method, the continuous underground wall method, and the injection method.

Among these construction methods, it is known that impermeable walls constructed using the continuous underground wall method have a low permeability coefficient and excellent impervious performance.

By the way, when constructing an impermeable wall using the continuous underground wall construction method, the excavation hole is filled with a stabilizing solution in which clay materials such as bentonite are suspended in water, and construction is carried out while preventing the wall from collapsing. When an excavation hole is formed to a predetermined depth, an impermeable wall is constructed by replacing the stabilizing liquid in the excavation hole with concrete and hardening the concrete. The water wall had problems as explained below.

<<Problems to be solved by the invention>> In other words, the impermeable wall constructed by the above-mentioned continuous underground wall construction method is made of hardened concrete, so it has a significantly lower coefficient of permeability than impermeable walls such as sheet piles. Although it varies depending on the type of concrete and the construction method, it is generally 10 ^-6 to ^{10 -8} cm/
The limit is sec.

However, for example, in impermeable walls for underground disposal of various types of waste such as radioactive waste, it is extremely necessary to prevent contamination of groundwater and soil, and for this purpose, the hydraulic conductivity coefficient is even lower than the above-mentioned hydraulic conductivity coefficient. Water-shielding walls are in demand, but there has been a problem in that conventional construction methods cannot meet this demand.

In addition, water-shielding walls made of hardened concrete have almost no ability to adsorb contaminants such as radioactivity, so if there are cracks or other defects in the water-shielding walls, there is a risk that this could be spread outside. .

This invention was made in view of these conventional problems, and its purpose is to:
It is an object of the present invention to provide a method for constructing a water-shielding wall that can construct a water-shielding wall that has a water permeability coefficient lower than that of conventional walls and also has the ability to adsorb contaminant components.

<Means for Solving the Problems> In order to achieve the above object, the present invention forms a borehole while filling it with a stabilizing liquid in which clay such as bentonite is suspended, and mixes the stabilizing liquid with a cement mixture. In the method for constructing an impermeable wall in which a continuous wall is sequentially constructed underground through replacement, after forming the excavation hole, an electrode plate is installed on the wall surface of the hole, and an electrode rod is installed in the excavation hole, and A DC positive electrode is connected to the electrode plate, while a DC negative electrode is connected to the electrode rod, and electricity is passed between these electrodes to form a water-stopping film made of the clay on the electrode plate side, and after this, The method is characterized in that the cement mixture is poured into the borehole.

<Operation> According to the construction method of the impermeable wall having the above configuration, before concrete is placed, an electrode plate is installed on the hole wall surface of the excavation hole filled with stabilizing liquid, and an electrode plate is installed inside the excavation hole. When the positive and negative electrodes of a DC voltage are connected between the fixed electrode rod and the current is applied, clay particles such as bentonite in the stabilizing liquid move to the electrode plate side and accumulate due to electroosmotic and electrophoretic phenomena. The clay particles form a highly concentrated water-stopping film.

Therefore, if concrete is then poured and hardened, a water-stop film will be formed on the outside of the concrete water-shielding wall, and the permeability coefficient of the water-shielding wall will become considerably small.

Furthermore, since the water-stop film is made up of clay particles accumulated at high density, each particle has a large surface area and has the ability to adsorb contaminants such as radioactivity.

<<Example>> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the method for constructing a water-blocking wall according to the present invention.

In the method for constructing an impermeable wall shown in the figure, first, a groove-shaped excavation hole 10 is formed (see FIG. 1a).

When drilling the borehole 10, a stabilizing liquid 1 in which clay such as bentonite is suspended is added to the borehole 10.
2, while preventing the wall of the excavation hole from collapsing, and the excavation is carried out to a predetermined depth to construct an impermeable wall.

When the excavated hole 10 is formed, as shown in FIG.
A pair of electrode plates 14, 14 are installed along 0a.

The electrode plate 14 is installed so as to cover almost the entire hole wall surface 10a, and its material is, for example,
In addition to metal thin plates, punched metal plates, wire mesh, etc., conductive sheets or meshes, and even carbon fiber meshes can also be used, and these materials preferably have a specific resistance of 10 ^-4 Ωm or less.

Further, in addition to bentonite, clay such as zeolite may be added to the stabilizing liquid 12, and more preferably, a clay material having ion adsorption properties is added.

Next, a plurality of metal electrode rods 16 are installed approximately at the longitudinal center of the excavated hole 10 at predetermined intervals.

The length of each electrode rod 16 is set to be approximately the same length as the electrode plate 14 described above.

Then, when the electrode plate 14 and the electrode rod 16 are installed at predetermined positions, the electrode plate 14 is connected to the DC power source 18.
Each electrode rod 16 is connected in series with a lead wire 22 and then connected to the negative electrode of a DC power source 18.

As a result, an electric field corresponding to the voltage of the DC power supply 18 is formed between the electrode plate 14 and the electrode rod 16, and the stabilizing liquid 12 exists in this electric field.

When the stabilizing liquid 12 exists in an electric field, clay particles such as bentonite in the stabilizing liquid 12 move to the positive electrode side, that is, the electrode plate 14 side, due to an electrophoretic phenomenon, and water in the stabilizing liquid 12 moves to the negative electrode side, That is, it moves toward the electrode rod 16 side.

When DC voltage is continued to be applied between the electrode plate 14 and the electrode rod 16, the clay particles gradually accumulate around the outer periphery of the electrode plate 16, and as shown in FIG. 1c, the clay particles are highly concentrated. A water-stop film 24 is formed.

In this case, the voltage of the DC power supply 18 is 10~
A voltage in the range of 200V is used, and the thickness of the water stop film 24 is preferably about 3 to 10 cm.

When the water stop film 24 is formed to a predetermined thickness, the first
As shown in Figure d, concrete 26 is placed in the excavated hole 10, and the stabilizer 12 and concrete
When the concrete is replaced and the poured concrete hardens, a panel-shaped wall is constructed.After that, by repeating the above steps one after another, the panel-shaped walls are connected laterally to form a predetermined length. A water-blocking wall will be constructed.

Here, the water-stop membrane 24 is pressed against the hole wall surface 10a side by the casting pressure of the concrete 26, so that the clay particles can be further compacted.

Note that the electrode plate 14 and the electrode rod 16 may be removed or buried.

Now, in the impermeable wall constructed by the method described above, the water-stopping membranes 24, 24 are formed on both sides of the impermeable wall body made of concrete 26, so the permeability coefficient of the impermeable wall is quite small. Become.

According to the experiments conducted by the present inventors, the water-stop film 24 in which bentonite is accumulated by electroosmotic phenomenon,
It has been confirmed that a hydraulic conductivity of 10 ^-8 to 10 ^-10 cm/sec can be obtained.

In addition, the water-blocking wall in which the water-stopping film 24 is formed on the outside of the concrete 26 not only compensates for defects in the concrete wall during construction, but also ensures water-stopping properties even if cracks occur in the concrete wall after construction. .

Furthermore, since the water-stop film 24 is made up of clay particles accumulated at a high density, each particle has a large surface area.
It also has the ability to adsorb contaminants such as radioactivity.

In addition, although the above-mentioned embodiment illustrated the case where the water stop film 24 is formed on both sides of the concrete wall, the implementation of the present invention is not limited to this, and the water stop film 24 may be formed only on one side of the concrete wall. good.

<<Effects of the Invention>> As explained above in the embodiments, according to the method for constructing a water-blocking wall according to the present invention, a water-blocking film in which clay particles are accumulated is formed on the outside of a concrete wall, so that the coefficient of water permeability increases. A water-shielding wall that is smaller than conventional walls and has a function of adsorbing contaminant components can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the method of the present invention in the order of steps. 10... Excavation hole, 12... Stabilizing liquid, 14... Electrode plate, 16... Electrode rod, 18... DC power supply, 24
...Waterstop membrane, 26...Concrete.

Claims (1)

[Scope of Claims] 1. An impermeable wall in which an excavation hole is formed while being filled with a stabilizing liquid in which clay such as bentonite is suspended, and the stabilizing liquid is replaced with a cement mixture to sequentially construct a continuous wall underground. In the construction method, after forming the borehole, an electrode plate is installed on the wall of the borehole, an electrode rod is installed in the borehole, and a DC positive electrode is connected to the electrode plate, while the electrode A DC negative electrode is connected to the rod and electricity is passed between these electrodes to form a water-stopping film made of the clay on the electrode plate side, and then the cement mixture is poured into the excavation hole. How to construct a water-shielding wall. 2. The method for constructing an impermeable wall according to claim 1, wherein the electrode plates are installed on both sides of the wall surface of the excavated hole. 3. The method for constructing a water-blocking wall according to claim 1 or 2, wherein the electrode plate is made of a conductive sheet. 4. The method for constructing a water-blocking wall according to claim 1 or 2, wherein the electrode plate is made of a metal mesh. 5. The method for constructing a water-blocking wall according to claim 1 or 2, wherein the electrode plate is made of carbon fiber.