JP2003033759A - Contaminant spread prevention method using water retaining type underground wall - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method wherein a high spread prevention effect can be obtained in a comparatively easy way and at a low cost in a contaminant spread prevention method using a water retaining type underground wall. SOLUTION: An underground wall 1 is constructed such that is reaches a non-permeable layer U in such a way as to surround a contaminated area 1 to seal the contaminated soil at the original position. A space part 2 is excavated to the underground wall 1 itself and water is poured into its inner part. By always keeping the water level inside the space part 2 of the underground wall 1 higher than that of the peripheral underground water, a infiltration flow from the underground wall 1 having slight water permeability toward the peripheral ground, thereby preventing the contaminated underground water from passing through the underground wall 1 and spreading to the outside area O of the contaminated area. In order to prevent the inner wall of the space part 2 from collapsing, a filler 7 that does not damage permeability may be filled. Further, in order to ensure water stop performance of the underground wall 1, a liner sheet is installed inside the space part 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pollutant diffusion prevention method for isolating pollutants from the general environment and preventing the diffusion of pollutants to the surroundings by utilizing an underground wall having a slight water permeability. It is a thing.

[0002]

2. Description of the Related Art As an application regarding the measures for cleaning contaminated soil, for example, Japanese Patent Laid-Open Nos. 9-267082 and 10
For example, those described in JP-A-258266 and JP-A-10-277531 can be cited.

The invention described in Japanese Unexamined Patent Publication No. 9-267082 relates to a method for cleaning soil contaminated with a volatile organic compound, in which a cleaning area using microorganisms is formed in the contaminated area and Purification is achieved by a gas flow circulating in the purification region.

The invention described in Japanese Unexamined Patent Publication No. 10-258266 relates to a method for cleaning soil contaminated by organic waste such as oil in-situ, and a stop for enclosing a contaminated area with a water impermeable layer below and the surrounding area. The water is separated from the water wall, and washing water is supplied under pressure onto the impermeable layer, and the contaminants are taken into the washing water while flowing out to the surface of the earth for recovery.

The invention described in Japanese Patent Application Laid-Open No. 10-277531 relates to a purification method by groundwater circulation that can widely cope with various pollution situations and can reduce costs, and a water injection well surrounding a contaminated area. In addition, the pumping well will be installed so that the injected water will pass through the contaminated area, and the groundwater pumped from the pumping well will be treated by the above-ground pollution treatment equipment and returned to the ground from the water injection well.

On the other hand, according to the guidelines of the Environment Agency issued in February 1999, the basic policy of the in-situ containment policy of pollutants is as follows.

Underground layer thickness 5m or more, permeability coefficient 1.0 ×
There is an impermeable layer of 10 ⁻⁵ cm / sec or less.

The contaminated area is surrounded and closed by a work piece having a water stopping function. Specifically, a water-impervious structure is considered by constructing steel sheet piles and SMW underground continuous walls, but SMW underground continuous walls have a width of 50 cm or more and a hydraulic conductivity of 1.0 x 10
^-6 cm / sec or less. Also, install up to the underground impermeable layer.

When treating groundwater in a contaminated area, a treatment facility removes pollutants to below the environmental standard value and discharges them to the outside.

In order to prevent rainwater and the like from entering, a material having a high water blocking function is laid on the surface. Specifically, it is a double impermeable structure with a combination of impermeable sheet material and improved mixed soil layer.
In addition, when this structure is applied, the treatment by the treatment facility is not necessarily required.

In order to prevent the outflow / diffusion of pollutants outside the planned site, it is desirable to set the groundwater level inside and outside the SMW below the surrounding water level.

[0012]

According to the above basic policy, especially the countermeasures, it is possible to prevent the diffusion of pollutants, but the hydraulic conductivity of the constructed SMW depends on the construction situation at the site. There is a high possibility that the actual hydraulic conductivity with respect to the target value will vary due to the effects of weather and curing conditions.

Since SMW is constructed in muddy water, it is assumed that the voids inside the member are saturated with water, and the member itself is a material whose permeability can be measured. It is thought that an infiltration flow occurs in the.

Therefore, when the groundwater level inside the SMW is higher than the outside, there is a risk that the pollutants will diffuse out of the area.

As a countermeasure against these, the SM as described above is used.
Measures to lower the groundwater level in the W area have been considered, but to keep the groundwater level in the area below the outer groundwater level at all times,
It may be inefficient in terms of facilities such as pumping facilities and water level observation facilities.

The inventions described in the above-mentioned JP-A-9-267082 and JP-A-10-258266 are:
It is intended for specific pollutants and cannot be applied to various pollutants.

In the case of the invention described in Japanese Patent Application Laid-Open No. 10-277531, various kinds of pollution can be dealt with depending on the performance of the ground-based pollution control device. However, in the arrangement of the water injection well and the pumping well, the groundwater circulation path is provided. Is difficult to secure, and pollutants may spread to the surrounding area.

Further, the inventions described in the above publications do not satisfy the above basic policy of the measure for confining pollutants in the original position and are insufficient as an alternative method.

The present invention provides an efficient method for preventing the diffusion of pollutants, which is relatively simple and at low cost, in order to prevent the diffusion of the pollutants by utilizing the underground wall. The purpose is to do.

[0020]

The method for preventing the diffusion of pollutants according to claim 1 of the present application constructs an underground wall having a slight water permeability so as to surround a contaminated area, and the inside of the underground wall itself is constructed. The present invention is characterized in that water is held or a space for holding water is formed in the underground wall, and the water level of the water held is adjusted to be equal to or higher than the surrounding groundwater level.

Here, the fact that it has a slight water permeability basically means that S has been conventionally used as an impermeable wall.
It has a water-stopping property that satisfies a certain degree of demand, such as a MW underground wall, but does not mean that it is completely water-stopping, but means that permeation flow is allowed to occur in the wall.

Therefore, by setting the water level inside the underground wall to be equal to or higher than the groundwater level inside the underground wall, a seepage flow from the underground wall side to the contaminated area side is generated, resulting in pollution. It is possible to prevent contaminated groundwater in the area from penetrating outside the contaminated area through the underground wall.

In this case, the water level inside the underground wall is usually higher than the groundwater level outside the contaminated area, but basically it is sufficient if it is higher than the groundwater level in the contaminated area. In that case, it may be lower than the groundwater level outside the contaminated area.

In addition, when there is a large difference in groundwater level depending on the location even in the contaminated area, and when the groundwater level near the underground wall is low, the water level inside the underground wall is high relative to the entire contaminated area. It does not have to be, but it should be higher than the groundwater level near the underground wall. However, if the ground conditions are complicated and there is a seepage flow with a relatively high velocity underground, it may be necessary to consider it separately.

The space in the underground wall is the strength of the underground wall itself,
It is desirable to form as deep as possible within the range possible depending on the technical conditions for forming the space, cost, etc.
Depending on the conditions, it may be installed only above the underground wall.

As a method of forming the space portion, after the underground wall is constructed, the groove portion is excavated, or the space portion is excavated by an excavation device capable of boring, and the space portion is formed in advance. It is conceivable to embed the above-mentioned member in the underground wall and then pull it out to form a space part, or to attach a member that forms another space part to the top of the underground wall, etc., depending on the site conditions, design, etc. It can be used properly depending on the situation.

Further, the space portion is not limited to be continuous in the wall direction of the underground wall, and when the space portion is divided into a plurality of space portions or a plurality of hole-shaped space portions, further, the divided space portions are separated from each other. Various cases are conceivable, such as the case of communicating at the middle or upper part in the depth direction.

According to a second aspect of the present invention, in the method for preventing diffusion of contaminants according to the first aspect, in order to ensure water permeability, a space portion is formed by a groove or a hole in the underground wall, and a filler is filled in the space portion. It is limited to the case of being filled.

As the filler, sand, crushed stone or gravel having good water permeability, or any other material capable of ensuring water permeability by forming voids or the like can be used. By filling with the filling material, it is possible to prevent the inner wall surface of the space portion from collapsing.

A third aspect of the present invention is the method for preventing the diffusion of pollutants according to the first or second aspect, which limits the case where a water barrier sheet extending in the in-plane direction of the underground wall is installed in the space. .

As the water blocking sheet, for example, a vinyl sheet or the like can be used, but the material, thickness, water stopping performance, etc. are not particularly limited.

In the present invention, it is not expected that the underground wall itself is completely waterproof, and it is premised that an infiltration flow occurs in the wall body. Therefore, by arranging the water-impervious sheet two-dimensionally or in an arbitrary form in the space portion of the underground wall, it is possible to enhance the water stopping property of the entire underground wall.
In this case as well, the water stopping property is not required to be completely water stopping, and includes ones that bypass the path of the osmotic flow in the wall body and those that substantially reduce the water permeability.

A fourth aspect of the present invention is the method for preventing the diffusion of pollutants according to the first, second or third aspect, wherein the permeability coefficient of the underground wall is 1.0 × 10 ⁻⁷ cm / sec or more and 1.0 × 10 ^{−. 5} cm /
It is limited to the case of being less than a second.

According to the basic policy of the containment measures described in the section of the prior art, the width of the SMW underground continuous wall as an impermeable wall is 50 cm or more and the hydraulic conductivity is 1.0 × 10 ^-6 cm / sec or less. However, due to the fact that there are variations and that soil mortar systems and other underground continuous walls other than SMW underground continuous walls can also be used, etc.
Then, the permeability coefficient of the underground wall is 1.0 × 10 ^-7 cm / sec or more,
It was set to 1.0 × 10 ⁻⁵ cm / sec or less. However, since the water-stop performance varies depending on the wall thickness and material of the underground wall, the presence or absence of a water-blocking sheet, etc., the target water permeability coefficient may be set according to the conditions.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows an embodiment in which the present invention is applied to shallow layer pollution.
The underground wall 1 is constructed so as to surround the contaminated area I.
The underground wall 1 reaches the impermeable layer U, and basically, the underground wall 1 and the impermeable layer U form a closed space, which has a structure in which pollutants are contained in the original position.

When the contamination area is relatively shallow, or when the underground impermeable layer U is in a shallow layer, after the underground wall 1 is constructed,
By excavating the space part 2 in the underground wall 1 itself, injecting water into the space part 2 and always keeping the water level inside the space part 2 above the surrounding groundwater level, it is possible to effectively prevent the diffusion of pollutants. be able to. Regarding the space portion 2, for example, in the case of an SMW underground wall having a wall thickness of about 70 cm, by setting the width to about 10 to 15 cm, it is possible to implement the present invention in a form in which the strength of the underground wall is not significantly impaired. Become.

As shown in FIG. 1 (c), sand or crushed stone with good water permeability in the space 2 is used for curing the excavated portion.
It is also conceivable to fill it with a filling material 7 such as gravel.

It is also possible to install a water blocking material such as a water blocking sheet in the excavated space 2 in order to ensure the water blocking function.

In this embodiment, FIG. 1 (a)
As shown in Fig. 1, a pumping facility 3 such as a water collecting well is provided in the contaminated area I, the contaminated groundwater is pumped to the ground, treated by the treatment plant 4, and then appropriately treated. The part is used as water for pouring water into the space part 2 of the underground wall 1.

However, if the permeation into the outside O of the contaminated area is a problem, the permeation into the contaminated area I is directly carried out to form a circulation path between the pumping facility 3 and the treatment plant 4, and this circulation is By repeating the process, it is possible to gradually remove pollutants in the soil and purify the contaminated soil. Also,
The surplus treated water having a low pollution level and the pollutants removed after being treated in the treatment plant 4 can be carried out and disposed of outside the region depending on the conditions.

In addition, the surface of the contaminated area I is to be provided with a surface impervious work 5 for preventing the infiltration of rainwater into the ground, if necessary. As for this surface impermeable work, those indicated by the guidelines and the like can be used.

FIG. 2 schematically shows an embodiment in which the present invention is applied to deep pollution, and in this case also, the underground wall 1 reaching the impermeable layer U so as to surround the contaminated area I. Is constructed to contain contaminated soil in situ.

When the contamination area is relatively deep, or when the impermeable layer U is deep, it is difficult to excavate the deep space 2 in the underground wall 1 itself. In this example, instead of excavating the space portion, a water retention facility 6 for forming the space portion 2 is separately provided at the top end portion of the underground wall 1 so that water can be supplied to the inside of the water retention equipment 6. By keeping the internal water level of 2 above the surrounding groundwater level, we tried to prevent pollution diffusion.

The water retention facility 6 may be, for example, a concrete wall such as SMW that is added to the underground wall 1, or a panel made of metal or resin.

Further, FIG. 2 (c) shows a case where the filler 7 is put into the space 2 formed by the water retention facility 6 as in the case of the embodiment of FIG. The permeation holes 8 are formed so that the water supplied to the top end of the underground wall 1 is permeated, and the water pressure corresponding to the increased water level effectively acts on the deep portion of the underground wall 1. .

In addition, the concept of the pumping facility 3, the treatment plant 4, the surface impervious works 5, etc. is the same as in the embodiment of FIG. 1, and these facilities may or may not be required depending on the conditions. It is possible to install the equipment of.

FIG. 3 schematically shows another embodiment in which the present invention is applied to deep pollution, and in this case also, the underground wall reaching the impermeable layer U so as to surround the contaminated area I. No. 1 is constructed to confine the contaminated soil in its original position.

As described above, it is difficult to excavate a deep space in the underground wall 1 itself when the contamination range is relatively deep and the impermeable layer U is deep, but the underground wall is difficult to excavate. When a steel material or the like to be the core material is embedded in 1, the core material is removed, water is poured into the opening 9 after the removal, and the internal water level of the underground wall 1 is always kept above the surrounding groundwater level. Thus, it is possible to prevent the diffusion of pollution.

In this case, it is conceivable to apply a release agent or the like to the core material in advance or attach a release material so that the core material can be easily removed.

Further, as in the case of the embodiment shown in FIGS. 1 and 2, it may be possible to add a filler having good water permeability such as sand for curing the opening 9. In that case, the core material is made to facilitate the peeling work as described above, and the core material itself is provided with a hollow structure and the filler is placed therein.
By adopting a structure in which the filler is extruded from the tip of the core at the same time when the core is pulled out, the filler can be easily introduced without damaging the underground wall 1 itself.

In addition, when removing the core material, if the underground wall 1 does not collapse, a water blocking material such as a water blocking sheet may be inserted into the opening 9 in order to secure a more reliable water blocking function. Conceivable.

If the material or shape having water permeability is used as the core material, the water permeability can be secured by the core material.

In addition, the concept of the pumping facility 3, the treatment plant 4, the surface water-blocking work 5, etc. is the same as in the case of the embodiment of FIGS. 1 and 2.

[0054]

EFFECTS OF THE INVENTION The conventional groundwater level lowering method for preventing pollution diffusion is a planar and wide-area water level lowering measure in a contaminated area, whereas by raising the water level only in the underground wall, It is possible to effectively avoid the spread of pollution outside the area.

Since it is only necessary to adjust the water level locally, it is possible to reduce the required amount of water injection and reduce the cost required for maintenance.

According to the second aspect of the present invention, since the filling material capable of ensuring water permeability is filled in the space portion of the underground wall, it is possible to prevent the inner wall surface of the space portion from collapsing due to excavation of the space portion or the like. .

According to the third aspect of the present invention, by installing the water-blocking sheet extending in the in-plane direction of the underground wall in the space,
It is possible to improve the waterproofness of the underground wall having a slight water permeability, and prevent the diffusion of contaminated soil more reliably from the viewpoint of waterproofing.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, in which (a)
Is a vertical cross-sectional view showing the outline of the whole, (b) is a schematic cross-sectional view showing the basic structure of the underground wall part that forms the space part, and (c) is a cross-sectional view when the space part is filled with a filler. Is.

FIG. 2 shows another embodiment of the present invention,
(a) is a vertical cross-sectional view showing the outline of the whole, (b) is a schematic cross-sectional view showing the basic structure of the underground wall part forming the space part,
(c) is a cross-sectional view when the space is filled with a filler.

FIG. 3 is a vertical cross-sectional view showing an outline of the whole of still another embodiment of the present invention.

[Explanation of symbols]

I ... contaminated area, O ... outside polluted area, U ... impermeable layer, W ... groundwater level, 1 ... underground wall, 2 ... space part, 3 ... pumping facility, 4 ...
Treatment plant, 5 ... Surface water barrier, 6 ... Water retention facility, 7 ... Filler, 8 ... Penetration hole, 9 ... Opening part

Claims (4)

[Claims] 1. An underground wall having a slight permeability is constructed so as to surround a contaminated area, and the water level of the water retained in the underground wall is adjusted to be equal to or higher than the surrounding groundwater level. A method for preventing the spread of pollutants, which is characterized by the following. 2. The method for preventing diffusion of pollutants according to claim 1, wherein in order to ensure water permeability, a space portion is formed by a groove or a hole in the underground wall, and the space portion is filled with a filler. 3. The method for preventing the diffusion of pollutants according to claim 2, wherein a water-blocking sheet spreading in the in-plane direction of the underground wall is installed in the space. 4. The hydraulic conductivity of the underground wall is 1.0 × 10 ^−7.
The method for preventing diffusion of pollutants according to claim 1, 2 or 3, wherein the content is cm / sec or more and 1.0 × 10 ^-5 cm / sec or less.