JP2014133217A - Construction method for fixing contaminant in soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method for fixing contaminants in soil, in which method the contaminants can be adsorbed extremely effectively, when the contaminants exude from the contaminated soil, to prevent the elution thereof to underground water, and which method is simple.SOLUTION: The construction method for fixing contaminants in soil comprises the steps of: laying a water barrier layer, at the least, on the lower surface of the contaminated soil so that the water barrier layer is inclined downward from the outer peripheral side of the lower surface of the contaminated soil toward the inside thereof; laying an adsorption layer at the position of the lowermost part of the obliquely-laid water barrier layer; and laying the contaminated soil on both of the water barrier layer and the adsorption layer.

Description

  The present invention relates to a method for fixing contaminants in soil, and more particularly to a method for fixing contaminants in soil provided with an adsorption layer that effectively adsorbs contaminants such as heavy metals from the soil.

Natural or artificial contaminants are contained in the soil, and conventionally, the excavation backfill method and the in-situ insolubilization method are generally used as methods for insolubilizing and immobilizing contaminants in contaminated soil. It has been.
The excavation backfilling method, for example, excavates contaminated soil, mixes the excavated soil with an insolubilizing agent, performs insolubilization treatment, and then backfills the excavated soil to which the insolubilization treatment has been applied to the excavated location. It is a construction method.
The in-situ insolubilization method is a method for insolubilizing contaminated soil by, for example, kneading the contaminated soil with a kneader while supplying an insolubilizing agent.

  As construction methods used for embankment and landfill using residual soil containing pollutants, (1) a method of constructing a water-impervious structure and water collection structure under the contaminated soil and treating the collected water ( 2) There is a method of laying a chemical adsorbing pollutants under the contaminated soil.

  As a method for insolubilizing the contaminated soil, for example, as described in JP 2012-125668 A (Patent Document 1), a contaminated soil is filled with a liquid insolubilizer to insolubilize the contaminated soil. A method for in situ soil insolubilization, wherein a water-impervious wall constructing step for constructing a water-impervious wall surrounding the contaminated soil in the ground, and the soil inside the water-impervious wall is filled with a liquid insolubilizer and the contaminated soil In-situ insolubilization method for contaminated soil, characterized by comprising an insolubilizing agent filling step for saturating the soil with the insolubilizing agent.

  JP 2011-194372 A (Patent Document 2) discloses a management structure of insolubilized soil obtained by insolubilizing soil contaminated with cyan, and the insolubilized soil and surrounding soil. There is disclosed a management structure for insolubilized soil, characterized in that a neutralization layer made of an alkaline material is provided between them, and further, a water shielding layer is provided between the neutralization layer and the insolubilized soil. Yes.

  JP 2010-29769 A (Patent Document 3) discloses an in-situ containment method for constructing a water-impervious wall that reaches an impermeable layer or a hardly permeable layer so as to surround the sewage area and contain the contaminated soil in the contaminated area. And a groundwater purification means through which groundwater in the inner area of the impermeable wall is passed, and the purifying means so that the groundwater level in the inner area of the impermeable wall is lower than the groundwater level in the outer area of the impermeable wall. An in-situ containment method is disclosed, in which purified water from the water is discharged to the outer region of the impermeable wall.

  In the construction method in which an adsorption layer for adsorbing contaminants in contaminated soil (hereinafter referred to as “adsorption layer construction method”) is used, for example, when heavy metal-containing soil is enclosed in the embankment, There is no particular problem as long as the concentration of contaminants discharged from the bottom surface of the soil-absorbing layer is below the reference value.

However, in the conventional adsorption layer construction method, in general, if the embankment collapses or cracks, or if the adsorption layer that adsorbs the contaminants cracks, the contaminants from the heavy metal-containing soil There is a risk that osmotic water exceeding the amount of leached out and eluted into the groundwater to contaminate the groundwater.
Also, if a crack occurs in the adsorption layer, water with low pH from the heavy metal-containing soil leaches out into the well-known soil, and as a result, lead, arsenic, cadmium, hexavalent chromium that originally existed in the soil There is also a concern that harmful heavy metals such as ionize and elute into groundwater.

  In addition, a construction method that suppresses leaching of contaminants by providing a water shielding layer on the contaminated soil below the second elution amount or the contaminated soil below the second elution amount due to insolubilization (hereinafter referred to as “water seepage containment construction method”). However, when a double sheet is necessary, the installation cost is enormous, and a wastewater treatment facility is also required, which requires a large apparatus.

JP 2012-125668 A JP 2011-194372 A JP 2010-29769 A

  The object of the present invention is to solve the above-mentioned problems, without requiring a large device or the like, effectively preventing the pollutant from eluting into the groundwater together with the leachate even if there is a crack in the embankment, etc. The object is to provide a simple method for fixing pollutants in soil that can be concentrated and trapped very efficiently.

  This invention discovered the construction method which can capture a pollutant in an adsorption layer intensively reliably by devising the laying position of the impermeable layer provided in the lower part of contaminated soil.

That is, the method for fixing pollutants in soil of the present invention is
Laying a water shielding layer on at least the lower surface of the contaminated soil by inclining downward from the outer peripheral side of the lower surface of the contaminated soil to the inside,
An adsorption layer is laid at the lowermost position of the water-impervious layer laid obliquely and above the groundwater surface,
A method for fixing pollutants in soil, comprising laying contaminated soil on the water shielding layer and the adsorption layer.

  Preferably, in the method for fixing contaminants in soil according to the present invention, the adsorption layer is laid with a capacity 1.3 to 1.5 times the theoretical adsorption amount of the contaminants contained in the contaminated soil. This is a method for fixing pollutants in soil.

Preferably, in the method for fixing pollutants in soil of the present invention, the water shielding layer is further laid on the side surface of the contaminated soil.
Still further, in the method for fixing contaminants in soil according to the present invention of the present invention, the upper surface of the contaminated soil laid on top of the water shielding layer and the adsorption layer is a water shielding layer laid on the lower part of the contaminated soil. It is a method for fixing pollutants in soil, characterized by being narrower than the surface connecting the upper ends of the soil.

  Here, “contaminated soil” includes both soil in which contaminants such as heavy metals have been insolubilized and contaminated soil prior to insolubilization. Final revision: July 8, 2011, Ministry of the Environment Ordinance No. 13) Article 9, Paragraph 1, Item 2 and the attached table 2)) The following contaminated soil and contaminated soil that became less than the second leaching amount due to insolubilization treatment Is included.

According to the method for fixing pollutants in soil of the present invention, it is possible to effectively prevent the pollutants from eluting into the groundwater together with the leachate even if cracks or the like enter the embankment without requiring a large device or the like.
Moreover, it can be a very simple construction method, and it becomes possible to adsorb and capture contaminants efficiently and reliably.

It is a figure which shows typically the side cross section for demonstrating embodiment of the 1st backfill structure of the pollutant fixation method in the soil of this invention. It is a figure which shows typically the side cross section for demonstrating embodiment of the 2nd backfill structure of the pollutant fixation method in the soil of this invention. It is a figure which shows typically the side cross section for demonstrating embodiment of the embankment structure of the pollutant fixation construction method in the soil of this invention.

The present invention is illustrated by the following preferred examples, but is not limited thereto.
The method for fixing pollutants in soil of the present invention is as follows.
Laying a water shielding layer on at least the lower surface of the contaminated soil by inclining downward from the outer peripheral side of the lower surface of the contaminated soil to the inside,
An adsorption layer is laid at the lowermost position of the water-impervious layer laid obliquely and above the groundwater surface,
A method for fixing pollutants in soil, comprising laying contaminated soil on the water shielding layer and the adsorption layer.

Based on FIG.1 and FIG.2, the contaminant fixing method in the soil of this invention is demonstrated.
FIG.1 and FIG.2 shows the example which applied the pollutant fixing method in the soil of this invention to the backfill structure.
In FIG. 1 as an example of the present invention, G is the ground, and shows a structure in which contaminated soil 1 that is soil containing contaminants such as heavy metals is backfilled in a depression.
On the bottom surface portion 5 of the contaminated soil 1, the water shielding layer 3 is laid so as to incline from the outer periphery of the bottom surface portion 5 of the contaminated soil 1 to the inside, preferably toward the bottom toward the center.
By laying the water shielding layer in this way, the water containing the pollutant can be intensively and efficiently adsorbed to the adsorption layer 2, and the water containing the pollutant is leached into the surrounding soil. Suppress.

Preferably, the upper surface 6 of the contaminated soil is structured to be narrower than the surface 7 connecting the upper ends of the water-impervious layer 3 laid on the lower portion of the contaminated soil 1.
By doing in this way, even if the pollutant contained in the contaminated soil 1 is dissolved and lowered in the water, the permeated water in which the pollutant is dissolved falls in the plane connecting the upper ends of the water shielding layers 3. And no leakage to the outside.

  Contaminants contained in the soil are, for example, type 2 specified hazardous substances (heavy metals) stipulated in the Soil Contamination Countermeasures Law. Specifically, cadmium, hexavalent chromium, cyan, mercury, alkyl mercury, selenium, Lead, arsenic, fluorine, boron, etc.

  As the water shielding layer applied to the method of the present invention, synthetic rubber, synthetic resin, asphalt, bentonite, cleaning compatible composite systems, steel sheet piles, bentonite, etc. clay, concrete, water tightness Asphalt concrete or the like can be used. These may be used alone or in combination.

The adsorption layer 2 having a certain thickness is laid at the lowest position of the water shielding layer 3 laid under the contaminated soil.
The adsorption layer is installed so as to be located above the groundwater surface.
The adsorbed layer 2 collects the permeated water containing the pollutants collected from the water-impervious layer 3 and collects the pollutants efficiently in a concentrated manner so that the pollutants can be leached into the surrounding soil and groundwater. Prevents merging.

As the adsorbent used in the adsorption layer, any known adsorbent capable of adsorbing and removing the pollutants contained in the contaminated soil can be used, which allows water to pass through but can adsorb and hold the pollutants. Can be applied.
Examples of the adsorbent that can be used include various porous materials such as artificial zeolite, volcanic ash, rock wool, and cellulose, and insolubilizers, and these can be used alone or in combination.

Preferably, in the method for fixing contaminants in soil according to the present invention, the adsorption layer is laid with a capacity 1.3 to 1.5 times the theoretical adsorption amount of contaminants contained in the contaminated soil.
By laying such an amount of adsorbent, it is not necessary to replace the adsorption layer, and the pollutant in the contaminated soil is sufficiently adsorbed.

  Further, the adsorption layer 2 can be embedded by compacting the adsorbent to the extent that it has a water permeability coefficient that maintains a constant water permeability, and the adsorbent layer device is filled with the adsorbent. It is also possible to lay it. In the case of using an adsorbing device filled with an adsorbent, it can be easily replaced every time the adsorbent's ability to trap contaminants decreases.

Moreover, preferably, as shown in FIG. 2, a water shielding layer is further laid on the side surface 8 of the buried contaminated soil.
Thus, by providing a water-impervious layer also on the side surface of the contaminated soil, it is possible to more effectively prevent the permeated water in which the contaminant is dissolved from leaching into the surrounding soil.

  In particular, it is desirable to construct a cover layer 4 made of asphalt or concrete on the upper surface of the contaminated soil 1. Thereby, it becomes possible to suppress the water | moisture content by rain etc. permeating into the contaminated soil 1. FIG.

FIG. 3 shows an application of the method for fixing pollutants in soil according to the present invention to an embankment structure.
In FIG. 3 as an example of the present invention, G is the ground, and shows an embankment structure of contaminated soil 1 which is soil containing pollutants.
On the bottom surface portion 5 of the contaminated soil 1, the water shielding layer 3 is laid so as to incline from the outer periphery of the bottom surface portion 5 of the contaminated soil 1 to the inside, preferably toward the bottom toward the center.
By laying the water shielding layer in this way, the water containing the pollutant can be intensively and efficiently adsorbed to the adsorption layer 2, and the water containing the pollutant is leached into the surrounding soil. Suppress.

Preferably, the upper surface 6 of the contaminated soil is narrower than the surface 7 connecting the upper ends of the water-impervious layers 3 laid on the lower portion of the contaminated soil 1 in the case of FIG. Structure.
By doing in this way, even if the pollutant contained in the contaminated soil 1 is dissolved and lowered in the water, the permeated water in which the pollutant is dissolved falls in the plane connecting the upper ends of the water shielding layers 3. And no leakage to the outside.

  Contaminants contained in the soil are the same as those described in FIG. 1 and FIG. 2, and the same material as that described in FIG. 1 and FIG. Can do.

The adsorption layer 2 having a certain thickness is laid at the lowest position of the water shielding layer 3 laid under the contaminated soil.
The adsorption layer is installed so as to be located above the groundwater surface.
The adsorbed layer 2 collects the permeated water containing the pollutants collected from the water-impervious layer 3 and collects the pollutants efficiently in a concentrated manner so that the pollutants can be leached into the surrounding soil and groundwater. Prevents merging.
As the adsorbent used for the adsorbing layer, the same material as that described with reference to FIGS. 1 and 2 can be used.

Preferably, in the method for fixing contaminants in soil according to the present invention, the adsorption layer is laid with a capacity 1.3 to 1.5 times the theoretical adsorption amount of contaminants contained in the contaminated soil.
By laying such an amount of adsorbent, it is not necessary to replace the adsorption layer, and the pollutant in the contaminated soil is sufficiently adsorbed.

  Further, the adsorbing layer 2 can be embedded by compacting the adsorbent, and an adsorbing layer device filled with the adsorbent can be laid. In the case of using an adsorbing device filled with an adsorbent, it can be easily replaced every time the adsorbent's ability to trap contaminants decreases.

Also preferably, a water shielding layer or a cover layer formed of asphalt, concrete, or the like is further laid on the side surface 8 of the soiled contaminated soil 1 shown in FIG.
Thus, by providing a water-impervious layer, a cover soil layer or the like on the side surface of the contaminated soil, it is possible to effectively prevent moisture such as rain from entering the contaminated soil 1.

  In particular, it is desirable to construct a cover layer 4 made of asphalt, concrete, or the like on the upper surface of the contaminated soil 1. Thereby, it becomes possible to suppress the water | moisture content by rain etc. permeating into the contaminated soil 1. FIG.

  The method for fixing pollutants in soil according to the present invention can intensively adsorb and remove pollutants, such as harmful heavy metals, in the adsorption layer 2 and can efficiently prevent the pollutants from joining groundwater. .

  The method for fixing pollutants in soil according to the present invention can be applied to both backfilling and embankment structures, such as processing technology for contaminated soil generated in large quantities by excavation and construction work such as tunnels and dams, etc. It can be applied to the treatment technology of contaminated soil from buildings such as factories and constructed land such as houses.

DESCRIPTION OF SYMBOLS 1 ... Contaminated soil 2 ... Adsorption layer 3 ... Water shielding layer 4 ... Covering soil layer 5 ... Bottom part 6 of contaminated soil 7 ... Top surface of contaminated soil 7 ... Water shielding layer Surface G connecting the upper ends ...

Claims (4)

Laying a water shielding layer on at least the lower surface of the contaminated soil by inclining downward from the outer peripheral side of the lower surface of the contaminated soil to the inside,
An adsorption layer is laid at the lowermost position of the water-impervious layer laid obliquely and above the groundwater surface,
A method for fixing pollutants in soil, comprising laying contaminated soil on the water shielding layer and the adsorption layer.   The method for fixing pollutants in soil according to claim 1, wherein the adsorption layer is laid with a capacity 1.3 to 1.5 times the theoretical adsorption amount of pollutants contained in the contaminated soil. A method for fixing pollutants in soil.   The method for fixing pollutants in soil according to claim 1 or 2, wherein the water shielding layer is further laid on a side surface of the contaminated soil.   The method for immobilizing contaminants in soil according to any one of claims 1 to 3, wherein an upper surface of the contaminated soil laid on the water shielding layer and the adsorption layer is laid on a lower portion of the contaminated soil. A method for fixing pollutants in soil, which is laid so as to be narrower than the surface connecting the upper ends of the water layer.

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