JP5704742B2 - Contaminant diffusion prevention structure - Google Patents

Description

The present invention relates to a contamination component diffusion preventing structure that prevents diffusion of contamination components contained in contaminated soil.

Due to excavation and construction work such as tunnels and dams, a large amount of soil containing contaminants such as heavy metals (hereinafter referred to as “contaminated soil”) is generated. In order to prevent the contamination component contained in the contaminated soil from diffusing, as disclosed in Patent Document 1, a technique for containing the contaminated soil in the embankment and treating it is known.
Hereinafter, the technique disclosed in Patent Document 1 will be described with reference to the drawings. FIG. 12 is a schematic view schematically showing a conventional contamination component diffusion preventing structure disclosed in Patent Document 1. As shown in FIG.
In FIG. 12, 100 is a conventional pollution component diffusion prevention structure, G1 is the ground surface, G2 is a free underground water surface located below the ground surface G1, and 101 is an adsorption layer laid on the ground surface G1 containing an adsorbent for capturing the pollutant components. , S is a contaminated soil laminated on the upper layer of the adsorption layer 101, 102 is a bank covering the adsorption layer 101 and the contaminated soil S, and 103 is an asphalt or concrete cover layer formed on the surface of the bank 102.

  In the contamination component diffusion preventing structure 100 configured as described above, when there is rainfall or snow accumulation on the embankment 102 or the cover layer 103, rainwater or snowmelt permeates the embankment 102, and the permeated water that has passed through the embankment 102 is contaminated soil. Infiltrate S. While the permeated water passes through the contaminated soil S, contaminating components such as heavy metals contained in the contaminated soil S are eluted into the permeated water. While the permeated water containing the contaminating component passes through the adsorption layer 101, the contaminating component is captured by the adsorption layer 101. As a result, the contaminated soil S can be purified, the contaminated components are prevented from reaching the free groundwater surface G2, and the contaminated components are prevented from flowing out into the groundwater and diffusing.

Similarly to Patent Document 1, the technique disclosed in Patent Document 2 is a technique that prevents the contaminated components of the contaminated soil S from diffusing. In the technique disclosed in Patent Document 2, the adsorption layer 101 described with reference to FIG. 12 is composed of a mixture of an adsorbent that adsorbs contaminating components and a diluent such as gravel. In the mixture, the space velocity of osmotic water (flow rate of osmotic water ÷ volume of the mixture) is set to 60 (hr ⁻¹ ) or less. Thereby, the contaminating component is captured by the adsorbent while the permeated water passes through the adsorption layer 101, and the permeated water is purified. As a result, like the technique disclosed in Patent Document 1, the contaminated soil can be purified, and the contaminated components are prevented from flowing out into the ground water and diffusing.

JP 2009-279550 A JP 2010-5624 A

However, the above conventional techniques have the following problems.
(1) Although the speed at which water penetrates into soil (penetration speed) varies depending on the amount of rainfall and the amount of snow (hereinafter referred to as “rainfall, etc.”), the techniques disclosed in Patent Documents 1 and 2 are: The penetration rate could not be controlled. Therefore, when there is little rainfall, etc., and the infiltration rate is slow, the contaminating components contained in the infiltration water can be captured by the adsorbent, but when there is a lot of rainfall, such as heavy rain, and the infiltration rate is high, it is included in the infiltration water. There is a problem that it becomes impossible to capture the contaminated components with the adsorbent.
(2) When there is a lot of rainfall such as heavy rain, there is a high possibility that the seepage water that has passed through the contaminated soil will be discharged not only in the vertical direction but also in the horizontal direction. When the permeated water is discharged in the horizontal direction, the adsorbed layer formed in the vertical direction of the contaminated soil cannot capture the contaminating components. When the permeated water is discharged in the horizontal direction, as disclosed in Patent Document 2, it is necessary to provide an adsorption layer so as to surround the contaminated soil. In this case, since the volume of the adsorption layer increases, there is a problem that a large amount of adsorbent is required.

The present invention solves the above-described conventional problems, and can limit the amount of permeated water that passes through the poorly permeable material and permeates into the contaminated soil without being affected by the rainfall or the like. The contaminated components are trapped in the first adsorbent layer composed of an adsorbent in the same amount or less as the conventional one, and the contaminated components moving upward in the vertical direction from the contaminated soil are placed between the hardly permeable material and the contaminated soil. An object of the present invention is to provide a contamination component diffusion preventing structure that is adsorbed by a second adsorption layer embedded in the substrate and prevents diffusion of the contamination component .

In order to solve the above-described conventional problems, the contaminated component diffusion preventing structure and the contaminated soil purification method of the present invention have the following configurations.
The pollutant component diffusion preventing structure according to claim 1 has a moisture-permeable material that prevents water from passing therethrough and a water-impervious material disposed in an upper layer of the contaminated soil, and is buried in the lower layer of the contaminated soil and has the difficulty. A first adsorbing layer that adsorbs pollutant components contained in the permeable material and permeated water that has passed through the contaminated soil, and a polluted component contained in the contaminated soil that is embedded between the hardly permeable material and the contaminated soil are adsorbed. And a second adsorption layer .
With this configuration, the following effects can be obtained.
(1) The amount of penetrating water (penetration amount) that passes through the poorly permeable material and permeates into the contaminated soil is limited by the hardly permeable material disposed in the upper layer of the contaminated soil. The permeated water that has permeated through the hardly permeable material and the contaminated soil permeates into the first adsorption layer, but the amount of the permeated water is limited, so that the contaminating component contained in the permeated water is captured by the first adsorption layer.
(2) The permeated water that cannot pass through the poorly permeable material is not contaminated because it does not contact the contaminated soil located in the lower layer of the hardly permeable material. On the other hand, even when the amount of rainfall is large, the amount of permeated water that passes through the poorly permeable material is limited, so that the permeation rate is regulated. As a result, penetrating water that passes through the contaminated soil is unlikely to be discharged in the horizontal direction, and most of it penetrates in the vertical direction. The permeated water that permeates in the vertical direction permeates the first adsorption layer embedded in the lower layer of the contaminated soil, and the contaminating component is captured by the first adsorption layer.
(3) From the above, the permeated water that has passed through the contaminated soil can be prevented from being drained in the horizontal direction, and the contaminated components can be reliably captured by the first adsorption layer without being affected by the amount of rainfall. be able to. Moreover, since the amount of permeation of the first adsorption layer is limited by the hardly permeable material, the contaminating component can be captured without increasing the amount of the adsorbent constituting the first adsorption layer. Thereby, the diffusion of contaminating components can be prevented. Furthermore, by providing a hardly water-permeable material instead of a completely water-impervious structure, the contaminated soil can be purified by passing the permeated water through the contaminated soil.
(4) Contaminated components contained in contaminated soil move downward in the vertical direction along with the permeated water during rainfall, but move upward in the vertical direction as the permeated water evaporates and concentrate in fine weather. There is a possibility. Since the contaminating component moved vertically upward from the contaminated soil is adsorbed by the second adsorption layer, it is possible to prevent diffusion of the contaminating component accompanying the evaporation of the permeated water.

Here, the hardly water-permeable material is composed of a sheet-like member that has moisture permeability and allows permeation of appropriate rainwater without completely blocking the passage of permeated water. Specifically, a synthetic resin single layer, a composite sheet, a nonwoven fabric, or the like having a water permeability coefficient of 1 × 10 ⁻³ to 1 × 10 ⁻⁸ m / s is preferably used. For example, as a composite sheet, an AK apec sheet (registered trademark) manufactured by Asahi Kasei Geotech Co., Ltd. is preferably used. As the permeability coefficient of the poorly permeable material becomes larger than 1 × 10 ⁻³ m / s, there is a tendency that contaminated components contained in the permeated water pass through the first adsorption layer when there is a large amount of rainfall and the infiltration rate is high. It is done. As the water permeability coefficient becomes smaller than 1 × 10 ⁻⁸ m / s, there is a tendency that the amount of the permeated water passing through the hardly permeable material decreases and the contaminated soil is hardly purified with the permeated water. It is also possible to use a plurality of these synthetic resin single layers, composite sheets, nonwoven fabrics and the like.

  The first adsorption layer can be formed by laying an adsorbent. Any adsorbent can be used without particular limitation as long as it can adsorb contaminating components that adversely affect the human body among the components contained in the contaminated soil. For example, “Ecomel (registered trademark)” containing an iron-based compound, “Adcera (registered trademark)” containing a plurality of rare earth compounds mainly composed of cerium can be used, and Al, Fe, Si, Those containing one or more of P, Ca, Mg and the like, artificial zeolite, volcanic ash soil and the like can also be used. These can also be used by mixing with rock wool, cellulose-based filter media and the like.

Examples of contaminating components contained in the contaminated soil and trapped by the adsorbent include arsenic, fluorine, boron, selenium, lead, chromium, cadmium, manganese, antimony, nickel and the like. The pollution component diffusion prevention structure can be constructed by embankment on the ground surface. It is also possible to excavate the ground and build it underground.
The adsorbent composing the second adsorbing layer is the same as that of the first adsorbing layer described above, and a description thereof is omitted.

The invention according to claim 2 is the contamination component diffusion preventing structure according to claim 1, and has a configuration including a coarse layer formed in an upper layer of the hardly water-permeable material.
With this configuration, in addition to the operation obtained in the first aspect, the following operation can be obtained.
(1) Contaminating components contained in contaminated soil move downward in the vertical direction along with the movement of the permeated water during rain, but may move upward and concentrate in the fine weather as the permeated water evaporates. is there. Even if the pollutant component is moved upward in the vertical direction, the capillarity is blocked by the coarse layer formed in the upper layer of the poorly permeable material, so that the capillarity rise to the surface of the pollutant component can be suppressed. The diffusion of components can be prevented.

  Here, the coarse-grained layer is constituted by a member in which voids are formed between particles by filling crushed stone, gravel, brick waste, glass waste, shell waste, ceramic waste, etc., and capillary action is blocked. .

Invention of Claim 3 is the pollution component spreading | diffusion prevention structure of Claim 1 or 2, Comprising: The embankment which covers the said contaminated soil , the water stop material embed | buried under the said 1st adsorption layer, and water absorption a horizontal drain is embedded between the a waterproofing material has a sex first adsorption layer, the contaminated soil permeate passes drained disposed outside the embankment is guided to the horizontal drain And an adsorbing device in which an adsorbent for adsorbing the contaminating components contained therein is exchangeably filled .
With this configuration, in addition to the operation obtained in the first or second aspect, the following operation can be obtained.
(1) Since the water-stopping material is provided in the lower layer of the first adsorption layer, it is possible to prevent soil below the embankment bottom from being contaminated with contaminating components.
(2) After the first adsorbing layer captures the contaminating component of the initial permeated water containing the contaminating component having a relatively high concentration, the capturing ability of the contaminating component may deteriorate with time. Since the first adsorption layer is buried in the lower layer of the contaminated soil, it is impossible to exchange the adsorbent of the first adsorption layer whose capture ability has deteriorated. When the trapping ability of the first adsorption layer deteriorates, the permeated water containing the contaminating component flows out and the contaminating component diffuses. However, since the water-stopping material is buried under the first adsorbing layer, Osmotic water is prevented from flowing out to the lower layer than the water material.
(3) The permeated water that has reached the waterstop material is guided in the horizontal direction along the waterstop material by the horizontal drain. Contaminating components contained in the osmotic water are adsorbed by passing through the adsorbing device and are prevented from flowing out. Thereby, while being able to prevent the spreading | diffusion of a pollutant component, a contaminated soil can be purified over a long term.
(4) Since the adsorption device is disposed outside the embankment, it is easy to exchange the adsorbent. Thereby, even if it is a case where the adsorption agent of a 1st adsorption layer deteriorates with time and the capture capability of a contamination component falls, a contamination component can be captured with the adsorption agent of an adsorption | suction apparatus. Further, when the adsorbent capturing ability of the adsorbing device is lowered, the contaminating component can be reliably captured by exchanging the adsorbent.

Here, the water-stopping material is constituted by a member that blocks water permeation, such as a water-stopping material made of synthetic resin or synthetic rubber, or a cement solidifying material.
As a horizontal drain, in addition to a sand mat, a mat-like or rope-like water entangled with natural fibers (for example, disclosed in JP-A-11-172666 and JP-A-2001-3342) is used. Can be used.
As the adsorption device, one filled with the aforementioned adsorbent can be used. The adsorbing device is preferably configured so that the adsorbent can be replaced. This is because the contaminated soil can be purified over a long period of time by exchanging it every time the adsorbent trapping capacity decreases.

A method for purifying contaminated soil includes a soil permeation process that allows permeated water that has passed through a poorly permeable material that has moisture permeability to block water permeation to the contaminated soil, and permeated water that has permeated the contaminated soil through the soil permeation process. And a contaminating component capturing step of contacting the contaminating component with the adsorbent to adsorb the contaminating component contained in the contaminated soil.
With this configuration, the following effects can be obtained.
(1) The amount (permeation amount) of permeated water that permeates the contaminated soil is limited by the soil permeation step that permeates the permeated water that has passed through the poorly permeable material to the contaminated soil. As a result, since the permeation speed of the permeated water contacting the adsorbent in the adsorption layer can be limited, the contaminating component contained in the permeated water can be captured without imposing a burden on the adsorbent by the contaminated component capturing step. Thereby, contaminated soil can be purified.

According to invention of Claim 1, it has the following effects.
(1) The permeated water that has passed through the contaminated soil can be prevented from being drained in the horizontal direction, and the contaminated component can be reliably captured by the first adsorption layer without being affected by the amount of rainfall. It is possible to provide a structure for preventing the diffusion of pollutant components that can prevent the diffusion of water.
(2) Since the permeation amount of the first adsorption layer is limited by the hardly water-permeable material, it is possible to provide a contamination component diffusion prevention structure that can capture the contamination component without increasing the amount of the adsorbent constituting the first adsorption layer.
(3) Contaminant components that move upward in the vertical direction as the permeated water evaporates in fine weather are adsorbed by the second adsorption layer. Can be provided.

According to invention of Claim 2, in addition to the effect of Claim 1,
(1) Even if the pollutant moves upward in the vertical direction as the permeated water evaporates in fine weather, the capillarity is blocked by the coarse layer formed in the upper layer of the poorly permeable material. It is possible to provide a contamination component diffusion preventing structure that can suppress the capillary rise and prevent the contamination component from diffusing.

According to invention of Claim 3, in addition to the effect of Claim 1 or 2,
(1) The permeated water that cannot penetrate into the water-stopping material is guided horizontally along the water-stopping material by the horizontal drain, and the contaminating components contained in the permeated water are adsorbed by passing through the adsorption device. It is possible to provide a structure for preventing the diffusion of contaminating components that can prevent the diffusion and purify the contaminated soil over a long period of time.

The schematic diagram which shows typically the contamination component spreading | diffusion prevention structure in one embodiment of this invention 1 is an enlarged view showing a portion indicated by II in FIG. 1 is an enlarged view showing a portion indicated by III in FIG. Schematic diagram of rainfall infiltration experiment equipment Temporal change diagram of pH of leachate Temporal changes of leachate As and Pb elution values Schematic diagram of evaporation experiment equipment X-ray fluorescence analysis of each soil Content analysis of As and Pb in each soil (X-ray fluorescence analysis) Time-dependent change diagram of pH in surface soil dissolution test Time course of As and Pb in surface soil Schematic diagram schematically showing a conventional contamination component diffusion prevention structure

(Embodiment)
Hereinafter, a contamination component diffusion preventing structure according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view schematically showing a contamination component diffusion preventing structure according to an embodiment of the present invention, FIG. 2 is an enlarged view showing a portion indicated by II in FIG. 1, and FIG. It is an enlarged view which expands and shows the part shown by III of 1.
In FIG. 1, 1 is a structure for preventing diffusion of pollutant components according to the present invention constructed on the ground surface G1 as an embankment structure, 2 is an embankment on which earth and sand are raised, 2a is a bottom of the embankment facing the ground surface G1, and 2b is near the upper layer of the embankment 2 It is the upper part of the embankment.

1 and 2, 3 is a water-stopping material formed of a water-stopping material made of synthetic resin or synthetic rubber and laid on the upper surface of the embankment bottom 2a, 4 is a sand mat, a plastic drain (for example, Asahi Kasei Geotech Co., Ltd.) Manufactured by the trademark “Public Drain”), a horizontal drain formed on the upper surface of the water-stopping material 3 and formed of a water-absorbing fiber mat, a real fiber having good water permeability, a non-woven fabric having a high porosity, and the like. Reference numeral 5 denotes a first adsorbing layer constructed by including an adsorbent that adsorbs and fixes contaminating components in soil mixed with artificial zeolite, rock wool, etc., which is laid on the upper layer of the horizontal drain 4, and S is the first adsorbing layer 5. Contaminated soil that is deposited on the top surface and is generated by tunnel excavation or construction work, and contains contaminating components such as arsenic, lead, and cadmium.
1 and 3, reference numeral 6 denotes an adsorbent that is laminated on the upper layer 2b of the embankment deposited on the upper surface of the contaminated soil S and mixed with artificial zeolite, rock wool or the like to adsorb and fix contaminating components in the soil. The second adsorbing layer 7, which is laid on the upper surfaces of the embankment 2 and the second adsorbing layer 6, is made of a synthetic resin sheet or nonwoven fabric having a water permeability of 1 × 10 ⁻³ to 1 × 10 ⁻⁸ m / s. It is a hardly water-permeable material that is formed and has moisture permeability and prevents permeation without completely blocking the passage of permeated water. In the present embodiment, the product name “AK Apec Sheet (registered trademark)” (10) manufactured by Asahi Kasei Geotech Co., Ltd. ^-5 m / s equivalent water permeability, gas passes). 8 is a coarse-grained layer formed of crushed stone, gravel, brick waste, glass waste, etc. and laminated on the upper surface of the hardly water-permeable material 7, 9 is embankment, 10 is made of asphalt or concrete formed on the upper surface of the embankment 9, etc. It is a soil covering layer.
In FIG. 1, reference numeral 11 denotes an adsorbing device connected to the horizontal drain 4 and disposed outside the embankment 2, and 11 a is a contamination contained in the permeated water that is accommodated in the adsorbing device 11 and led to the horizontal drain 4 and drained. An adsorbent that adsorbs components.

  The construction of the contamination component diffusion preventing structure 1 configured as described above is as follows. First, the embankment bottom 2a is formed while raising and rolling the earth and sand on the ground surface G1, and then the water stop material 3 is laid and the horizontal drain 4 is disposed. . Subsequently, after forming the 1st adsorption layer 5, the contaminated soil S is piled up and the circumference | surroundings are covered with the embankment 2. Next, after forming the 2nd adsorption layer 6 on the upper surface of the embankment upper part 2b, the poorly permeable material 7 is formed so that the 2nd adsorption layer 6 and the upper surface of the embankment 2 may be covered completely. Next, after the coarse particle layer 8 is disposed on the upper surface of the hardly water-permeable material 7, the embankment 9 is formed, and the upper surface of the embankment 9 is covered with the soil covering layer 10. Finally, the suction device 11 is connected to the horizontal drain 4.

Next, the purification method of the contaminated soil S using the contamination component diffusion prevention structure 1 configured as described above will be described.
Rainwater that has fallen on the contaminated component diffusion prevention structure 1 penetrates into the coarse-grained layer 8 as permeated water from the surfaces of the cover layer 10 and the embankment 9 and is guided to the hardly water-permeable material 7. Since the hardly permeable material 7 has a permeability coefficient of 1 × 10 ⁻³ to 1 × 10 ⁻⁸ m / s, part of the permeated water passes through the hardly permeable material 7 and permeates the contaminated soil S (the soil Transmission step).
On the other hand, the remaining portion of the permeated water that cannot pass through the poorly permeable material 7 stays in the upper part of the hardly permeable material 7. Since the coarse-grained layer 8 is provided on the upper surface of the hardly water-permeable material 7, the permeated water staying at the upper part of the hardly water-permeable material 7 is moved in the horizontal direction and gradually drained to the outside of the embankment 2. Since this permeated water is not in contact with the contaminated soil S, the contaminated components are not diffused even if the permeated water is drained outside the embankment 2.
In addition, by making the water permeability coefficient of the hardly water permeable material 7 about 1 × 10 ⁻⁵ m / s, in the case of normal rainfall, depending on the amount of rainfall, about 20 to 50% of the rainfall amount is hardly permeable material. 7 can be moved horizontally (drainage), and in the case of heavy rain, 90% or more can be moved horizontally (drainage) along the hardly permeable material 7. In this way, the permeation amount is regulated by setting the water permeability coefficient of the hardly water permeable material 7.

Now, the permeated water that has permeated through the contaminated soil S in the soil infiltration step descends the contaminated soil S while dissolving the contaminating components, and reaches the first adsorption layer 5. Thereby, the contaminated soil S is gradually purified. Further, the contaminating component contained in the permeated water is captured by the adsorbent of the first adsorbing layer 5 while passing through the first adsorbing layer 5 (the contaminating component capturing step). This prevents the diffusion of contaminating components.
Note that the permeated water that permeates the contaminated soil S is restricted by the hardly permeable material 7 so that the permeation speed is not more than a predetermined speed, so that the horizontal movement is suppressed. As a result, it is possible to prevent the permeated water from being discharged outside the embankment 2 without passing through the first adsorption layer 5. Moreover, since the permeation speed of the permeated water that permeates the first adsorption layer 5 is also regulated, the contaminating component is reliably captured without imposing an excessive burden on the adsorbent of the first adsorption layer 5.

  Next, the permeated water that has passed through the first adsorption layer 5 is blocked from moving in the vertical direction by the water blocking material 3. If the adsorbent of the first adsorbing layer 5 deteriorates with time and the trapping ability of the contaminating component is lowered, the contaminating component remains in the permeated water that has passed through the first adsorbing layer 5. Even in such a case, the downward movement of the permeated water is blocked by the water blocking material 3, so that the permeated water containing the contaminating component is prevented from reaching the underground free water surface G2, and the diffusion of the contaminated component is prevented. Is prevented.

  The permeated water that has reached the water stop material 3 is drained to the outside of the embankment 2 along the water stop material 3 by the horizontal drain 4, and is introduced into the adsorbing device 11 connected to the horizontal drain 4. The permeated water introduced into the adsorption device 11 passes between the adsorbents 11 a accommodated in the adsorption device 11. Even if contaminated components are contained in the permeated water, it is captured by the adsorbent 11a accommodated in the adsorption device 11. Moreover, since the adsorption | suction apparatus 11 is arrange | positioned outside the embankment 2, replacement | exchange of the adsorption agent 11a is also easy. Thereby, even if it is a case where the adsorption agent of the 1st adsorption layer 5 deteriorates with time and the capture capability of a contamination component falls, a contamination component can be captured by adsorption agent 11a of adsorption device 11. Furthermore, when the capturing ability of the adsorbent 11a of the adsorbing device 11 is lowered, the contaminating component can be reliably captured by exchanging the adsorbent 11a. Therefore, the adsorbent with which the permeated water containing the contaminating component is brought into contact in the contaminated component capturing step is not limited to the adsorbent of the first adsorbing layer 5, and the adsorbent 11a of the adsorbing device 11 is also included.

  Next, the behavior of the permeated water at the time of fine weather will be described. In the contaminated component diffusion preventing structure 1, during fine weather, the contaminated component moves upward in the vertical direction as the permeated water in the contaminated soil S is warmed and evaporated. Since the moved contaminated component is adsorbed and captured by the second adsorption layer 6, it is prevented that the contaminated component is further diffused. Even if the contaminating component reaches the hardly water-permeable material 7, the capillary phenomenon is blocked by the coarse particle layer 8 formed on the upper layer of the hardly water-permeable material 7, so that the capillary rise of the contaminating component can be suppressed. , Can prevent the diffusion of contaminating components.

As described above, the contamination component diffusion preventing structure 1 according to the first embodiment has the following effects.
(1) The amount of permeation that passes through the hardly permeable material 7 and permeates into the contaminated soil S is limited by the hardly permeable material 7 disposed in the upper layer of the contaminated soil S. The permeated water that has permeated through the poorly permeable material 7 and the contaminated soil S permeates the first adsorption layer 5, but the amount of the permeated water is limited, so that the contaminated components contained in the permeated water are captured by the first adsorption layer 5. Is done.
(2) Since the amount of permeation is limited by the hardly permeable material 7, the contamination component is captured without increasing the amount of the adsorbent constituting the first adsorption layer 5 (without increasing the thickness of the first adsorption layer 5). it can. In addition, the contaminated component diffusion prevention structure 1 is not a completely water-impervious structure, but the permeated water 7 is passed through the contaminated soil S to purify the contaminated soil S by providing the poorly permeable material 7 in the upper layer of the contaminated soil S. be able to.
(3) Even when the amount of rainfall is large, the amount of permeated water that passes through the hardly permeable material 7 is limited, so that the permeation rate is regulated. As a result, the permeated water that passes through the contaminated soil S is unlikely to be discharged in the horizontal direction, and most of it penetrates in the vertical direction. The permeated water that permeates in the vertical direction permeates the first adsorption layer 5 embedded in the lower layer of the contaminated soil S. Thereby, the contaminated component can be reliably captured by the first adsorption layer 5 without being influenced by the rainfall amount or the like.
(4) Even if the contaminating component contained in the contaminated soil S is moved upward in the vertical direction along with the evaporation of the permeated water in fine weather, the capillarity is caused by the coarse particle layer 8 formed in the upper layer of the hardly permeable material 7. Since it is blocked, the capillary rise of the contaminating component can be suppressed, and the diffusion of the contaminating component can be prevented.

(5) Since the water blocking material 3 is embedded in the lower layer of the first adsorption layer 5, the permeated water is prevented from flowing out from the water blocking material 3 to the lower layer. Even when the capturing ability of the contaminating component by the first adsorbing layer 5 is deteriorated, the permeated water containing the contaminating component is prevented from flowing out to the free ground water surface G2 and diffusing the contaminating component.
(6) The permeated water that cannot penetrate into the water stop material 3 is guided in the horizontal direction along the water stop material 3 by the horizontal drain 4. Thereby, it is prevented that the moisture content of the embankment structure of the contamination component diffusion preventing structure 1 becomes high and collapses. Moreover, the contaminating component contained in the permeated water is adsorbed by passing through the adsorbing device 11, and the outflow is prevented. Thereby, while being able to prevent the spreading | diffusion of a contaminating component, the contaminated soil S can be purified over a long period of time by replacing | exchanging adsorption agent 11a as needed.
(7) The permeated water that cannot pass through the hardly water-permeable material 7 is drained in the horizontal direction along the hardly water-permeable material 7 by the coarse particle layer 8. Thereby, the drainage property of the upper layer from the hardly permeable material 7 can be improved, and the water content of the embankment structure of the contamination component diffusion preventing structure 1 is prevented from being collapsed.
(8) Even if the contaminated component contained in the contaminated soil S is moved upward in the vertical direction as the permeated water evaporates in fine weather, it is adsorbed by the second adsorption layer 6 formed in the upper layer of the contaminated soil S. Therefore, it is possible to prevent the diffusion of contaminating components accompanying evaporation of the permeated water.
(9) Contaminated components transferred from the contaminated soil S in the embankment 2 to the infiltrated water diffuse even under the influence of changes in weather conditions such as increase in the infiltrated water due to changes in rainfall and evaporation of the infiltrated water due to clear weather. This can be reliably prevented, the contaminated soil S can be purified over a long period of time, and the risk of diffusion of contaminating components to the outside of the embankment 2 can be reduced over the long term.

Moreover, according to the purification method of the above contaminated soil, it has the following effects.
(1) The amount of permeated water that permeates the contaminated soil S (the amount of permeation) is limited by the soil permeation step that permeates the contaminated soil S with the permeated water that has passed through the hardly permeable material 7. As a result, since the permeation rate of the permeated water that contacts the adsorbent 11a (or the first adsorbing layer 5) can be limited, the contaminating component contained in the permeated water is removed from the adsorbent 11a (or the first adsorbing layer 5) by the contaminating component capturing step. ) Can be captured without burden. Thereby, the contaminated soil S can be purified while preventing the diffusion of contaminating components.

1. Rain penetration test (Experimental Examples 1-3)
Next, a rainfall infiltration experiment will be described as an experimental example for confirming the effect of the present invention with reference to the drawings. FIG. 4 is a schematic diagram schematically showing a rainfall experiment apparatus.
In FIG. 4, 20 is an experimental tank used for a rain test, 21 is a rectangular parallelepiped soil tank of about 60 cm in length (left and right direction in FIG. 4), and 21a and 21b are erected in the earth tank 21 with a predetermined interval. A dividing plate that divides the tank 21 into three sections (Experimental Example 1, Experimental Example 2 and Experimental Example 3), 22a is a drain pipe formed at the bottom of the soil tank 21 in which the soil layer in Example 1 is formed, 22b Is a drain pipe formed at the bottom of the soil tank 21 where the soil layer is formed in Experimental Example 2, 22c is a drain pipe formed at the bottom of the soil tank 21 where the soil layer is formed in Experimental Example 3, and 23 is a standard Standard sand layer of sand (massite from Shimonoseki, Yamaguchi Prefecture) filled to the bottom of the soil tank 21 with a thickness of 5 cm, 24 is a contamination prepared by mixing 1 wt% of arsenic sulfide ore residue with standard sand Contaminated soil layer in which the soil is 5 cm thick and filled on the standard sand layer 23 25 is a standard sand layer filled with a standard sand of 10 cm in thickness on the contaminated soil layer 24, and 26 is a bean gravel (particle size of about 5 to 10 mm) filled with a thickness of 3 cm on the standard sand layer 25. It is a bean gravel layer. The standard sand layer 23, the contaminated soil layer 24, the standard sand layer 25, and the bean gravel layer 26 are laminated in the same manner in the three sections (Experimental Example 1, Experimental Example 2 and Experimental Example 3).

Reference numeral 27 denotes an adsorption layer formed in a part of the standard sand layer 23 in the soil layer in Experimental Example 2. The adsorbing layer 27 is prepared by mixing 10 wt% of a rock wool-based (MRW agent) adsorbent containing magnesium calcium silicate with standard sand, and is filled with a thickness of 3 cm. Therefore, in the soil layer in Example 2, the thickness of the standard sand layer 23 is 2 cm, and the adsorption layer 27 is formed between the standard sand layer 23 and the contaminated soil layer 24. 28 is not a complete water-impervious sheet disposed between the upper surface of the standard sand layer 25 and the lower surface of the bean gravel layer 26 in the soil layer in Experimental Example 1, but allows gas to pass therethrough and hardly penetrates and passes moisture. Water permeable material (permeability coefficient 1 × 10 ⁻⁵ m / s, trade name “AK APEC sheet” manufactured by Asahi Kasei Geotech Co., Ltd.), 29 is a drain pipe formed on the side of the earth tub 21, and the soil layer beans in Experimental Example 1 It is connected to the bottom of the gravel layer 28 (the upper surface of the hardly permeable material 28). 30 is an artificial rain apparatus, 31 is a housing whose upper surface is covered with the upper part of the earth tub 21, 31 a is a side wall of the housing 31, 31 b is a top plate of the housing 31, and 32 is a discharge port having a side wall 31 a Humidifier (trade name Ultrasonic PET bottle humidifier manufactured by CCP Corporation) that spouts fine water droplets disposed on the air together with air, 33 is a mesh made of a synthetic resin having an opening of 2 cm, 33a is a mesh 33 A needle-like protrusion 34 that protrudes in a needle-like manner downward on the node is a supersaturated chamber in which fine water droplets and air are mixed.

As for the elution value of the prepared contaminated soil, As was 0.099 mg / L, Pb was 0.011 mg / L, and the pH of the eluate was 5.7. The elution values of standard sand, bean gravel and adsorbent were all below the detection limit, and the pH of the eluate was 8.7, 3.7, and 11.0, respectively.
The hydraulic conductivity was 6.4 × 10 ⁻⁶ m / s for the contaminated soil, 3.6 × 10 ⁻⁵ m / s for the adsorption layer, and 3.2 × 10 ⁻⁵ m / s for the standard sand. The hydraulic conductivity of the contaminated soil is small because silt-like residues having a small particle size are mixed.

1.1 Experimental Method The experiment was performed by giving rain to the experimental tank 20 (the upper surface of the bean gravel layer 26) using a rain apparatus. The rain generation method is different from the conventional methods (capillary drop, spray, etc.) in that water vapor generated by the humidifier 32 is condensed on the mesh 33 and the vertical protrusions 33a to generate raindrops. When reproducing actual rainfall on a laboratory scale, for example, 5 mm / d rainfall of 1 m ² is a very small amount of 3.5 mL / min. Therefore, it becomes difficult to give as continuous rain, and usually, for example, the daily precipitation is given in a short time and is intermittently repeated. This newly devised method has the advantage that it can give a small amount of rainfall continuously and has high uniformity. In this experiment, using two humidifiers with a capacity of 500 mL / 5 to 6 h, it was operated continuously for about 14 hours a day, and it was possible to give rain equivalent to 5.8 to 7.4 mm / d.
During the experiment, rainfall was continuously given for 2 weeks in a pattern of giving 5 consecutive days and resting for 2 days within 1 week. During the experimental period, the leaching flow rate from 22a, 22b, 22c, 29 of each experimental tank was measured once a day, and heavy metal analysis was also performed. As an analysis method, 5 ml of nitric acid was added to 30 ml of a test solution obtained by an official method, and the sample was decomposed by microwave and then measured by ICP-MS. During the experiment, the temperature and humidity inside the earth tub were measured using a miniature temperature and humidity meter. The amount of rain applied to the experimental tank 20 was 5.8 to 7.4 mm / day. The temperature in the earth tub 21 during the experiment period was 21.5 to 26.0 ° C., and the humidity was 96.6 to 100% RH.
Further, As analysis of leachate from the drain pipes 22b and 22c was performed. The analysis of the leachate was performed by adding 5 mL of nitric acid to 30 mL of the test solution obtained by the official method, decomposing with microwaves, and measuring by ICP-MS.

1.2 Experimental Results As a result of measuring the leaching flow rate, 0 mL / day from the drainage pipe 22a (Experimental Example 1), 210 to 566 mL / day from the drainage pipe 22b (Experimental Example 2), and the drainage pipe 22c (Experimental Example 3) From 225 to 466 mL, and from the drainage pipe 29 (the poorly permeable material 28 of Experimental Example 1) was 600 to 972 mL / day. In Experimental Example 1, it is thought that as a result of the amount of permeation being restricted by the hardly permeable material 28, the leaching from the drain pipe 22a was eliminated.

FIG. 5 shows changes over time in the pH of leachate in the countermeasure drain pipe 22b and the non-measure drain pipe 22c. Since the pH of the leachate from the drainage pipe 22a in the measure against rainfall is 7.7, the pH of the leachate that has passed through the contaminated soil is greatly reduced (pH = 3.3 to 3.7). . After that, when passing through the adsorption layer, the pH increases (pH = 5.7 to 7.1).
FIG. 6 shows changes over time in the As and Pb concentrations of leachate in the countermeasure drain pipe 22b and the non-measure drain pipe 22c. First, focusing on Pb, the concentration is smaller than that of As, but the countermeasure (drainage pipe 22b (Experimental Example 2)) is smaller than the countermeasure (drainage pipe 22c (Experimental Example 3)). After 3 days, the Pb concentration of no countermeasure (drainage pipe 22c) increased, but it seems that high-concentration pore water was leached locally. Next, paying attention to the concentration of As, it can be seen that the concentration of the countermeasure (drainage pipe 22b) is clearly smaller than that of the countermeasureless (drainage pipe 22c). In this experiment, although the thickness of the adsorption layer is 3 cm, the adsorption performance greatly depends on the permeation speed, and therefore, a tendency to slightly increase in the process in which the permeation flow rate fluctuates is recognized.
From the above results, it was found that the adsorption layer basically using the MRW agent can remove and reduce As and Pb from the leachate that has passed through the contaminated soil, and a purification effect can be expected.
Next, the As concentration is 0.003 to 0.040 mg / L of leachate for countermeasures (drainage pipe 22b (experimental example 2)), and leachable water for no countermeasures (drainage pipe 22c (experimental example 3)) It was 0.042-0.064 mg / L. The soil layer of Experimental Example 2 includes the adsorption layer 27, whereas the soil layer of Experimental Example 3 does not include the adsorption layer. This difference appears in the results of As analysis of leachate. However, although the soil layer of Experimental Example 2 includes the adsorption layer 27, the As concentration varies from 0.003 to 0.040 mg / L. One of the causes of fluctuations in this As concentration is fluctuation in the amount of penetration. It was confirmed that by arranging the hardly water-permeable material 28 as in Experimental Example 1, the contaminated soil can be purified over a long period of time while restricting the amount of permeation and preventing the diffusion of contaminating components.

2. Evaporation experiment (Experimental Examples 4 and 5)
The evaporation experiment was carried out with the aim of confirming that the permeated water might rise in the capillaries and concentrate on the surface during the evaporation process, and at the same time, use an adsorbent as a countermeasure method to confirm the effect. .
2.1 Experimental Method FIG. 7 is a schematic diagram of an experimental apparatus for an evaporation experiment.
40 is an evaporation experimental apparatus, 41 is an experimental tank, 41a is a dividing wall for dividing the experimental tank 41, 42 is a drainage drain made of a synthetic resin sheet, 43 is a drainage pipe with a cock 43a of the drainage drain 42, 44 is a layer thickness of 5 cm Reference numeral 45 denotes a standard sand layer made of Shimonoseki mashed soil filled with 1 and a contaminated soil having a layer thickness of 10 cm prepared by mixing 1 wt% of iron sulfide ore residue containing arsenic with standard sand. The elution value was 0.099 mg / L for As, 0.011 mg / L for Pb, and the pH of the eluate was 5.7. 46 is an adsorption layer prepared by mixing 10 wt% of a rock wool-based adsorbent containing magnesium calcium silicate (referred to as MRW agent) with standard sand, 47 is a halogen heater with an output of 800 W, 48 is a reflector made of an aluminum plate, 49 Is a water supply tank connected to the drainage drain 42 and a water supply pipe 49a, 49b is an overflow pipe of the water supply tank 49, and 50 is an external water supply tank.
The inside of the experimental tank 41 is divided into two countermeasures (with an adsorption layer, E1 tank, Experimental Example 4) and no countermeasures (without an adsorption layer, E2 tank, Experimental Example 5).
The conditions for evaporation were the water level set to 8 cm from the ground surface in conjunction with the water level of the external water supply pipe 50, and the room temperature set to 20 ± 1 ° C. Further, assuming evaporation promotion by solar radiation, irradiation was performed for 6 hours from 9:00 to 15:00 using a halogen heater. The maximum temperature near the soil layer surface at this time was about 27 ± 2 ° C. The amount of evaporation was determined by measuring the amount of decrease in the external water tank 50 once a day. As a result, a substantially stable evaporation amount was obtained, and the average was 2.2 mm / d. Generally, about 1/3 of the rainfall is supposed to be evapotranspiration, and if the precipitation is 1800 mm / y, it is 1.64 mm / d. During the experiment, the topsoil was divided, and soil collection was started 21 days after the start of the experiment, and data was acquired up to 85 days after several days. Moreover, the soil component analysis by the fluorescent X ray analyzer was performed using the surface soil after 50 days and 81 days.
2.2 Experimental results From the observation results of the experimental situation, the surface of the non-measure (E2 tank) has turned brown with time. For this reason, in order to investigate the cause, fluorescent X-ray analysis of surface soil was performed. FIG. 8 shows the results of content analysis of contaminated soil, standard sand, and experimental surface soil. Looking at this, it can be seen that Ca, K, and Fe are high. K does not change much in each soil, but Ca is a countermeasure (E1 tank) and Fe is high without countermeasure (E2 tank). Yes. The reason why Ca is high in the countermeasure (E1 tank) is that the acid contaminated soil passing water and the MRW agent used in the adsorption layer reacted, and the neutralized product calcium sulfate moved and precipitated in the surface soil. It is believed that there is. The reason why Fe is increased without countermeasures (E2 tank) is presumed to be that iron sulfate produced by oxidation of iron sulfide ore powder contained in the contaminated soil moved and deposited on the surface soil. Moreover, it is thought that the surface color of the non-measure (E2 tank) changed to brownish brown was a result of further oxidation of a portion of the iron sulfate that had moved to the surface soil to produce brownish iron hydroxide. FIG. 9 shows the contents of only As and Pb. From this, it can be seen that Pb does not change much, but As increases without countermeasures. This is considered to indicate that As is more mobile than Pb, and is moving from the contaminated soil to the surface layer and being concentrated as the water evaporates.
FIG. 10 shows the pH in the surface soil dissolution test. Looking at the figure, the pH is as high as 6 to 11 although there is a change in the countermeasure (E1 tank). With no countermeasure (E2 tank), the pH is 4 or less. It is thought that the effect of high pH (11.2) of the adsorption layer appears in the countermeasure (E1 tank), and the influence of low pH (5.7) of the contaminated soil appears in the non-measure (E2 tank). . FIG. 11 shows temporal changes in As and Pb of the surface soil. When attention is paid to As, it can be confirmed that there is a large variation compared to the countermeasure (E1 tank) although there is a large variation in the non-measure (E2 tank). As a cause of the fluctuation, it is surmised that the capillary rise / concentration may be uneven due to the subtle changes in the standard sand density. Next, when looking at Pb, all have low concentrations and no clear difference is observed.
From the above, it was confirmed that the moisture in the soil moved toward the surface due to the evaporation of the surface, and As or the like having a high mobility might move and concentrate upward. Moreover, it was found that the upward movement / diffusion of As may be suppressed by installing an adsorption layer using an MRW agent above the contaminated soil.

Although the present invention has been described based on the embodiments, the present invention is not limited to the above embodiments.
In the above embodiment, the case where the contamination component diffusion preventing structure 1 is configured by embankment on the ground surface G1 is described. However, the structure is not necessarily limited to this, and the ground surface G1 is excavated and configured in the excavated portion. Is also possible. In this case as well, the same effect can be obtained by disposing the poorly permeable material 7 in the upper layer of the contaminated soil S.
In the above embodiment, the case where the coarse-grained layer 8 is provided on the upper surface of the hardly permeable material 7 has been described. However, the present invention is not necessarily limited to this, and the coarse-grained layer 8 is partially provided according to the drainage property. It is also possible not to arrange them.

  The present invention relates to a treatment technique for contaminated soil generated in large quantities due to excavation work or construction work such as tunnels and dams, etc., and changes in weather conditions such as increase in permeated water due to changes in rainfall and evaporation of permeated water due to clear weather Even if it is affected, it is possible to reliably prevent the contaminated components that have migrated from the contaminated soil to the permeated water from diffusing and to purify the contaminated soil over a long period of time, thereby contributing to environmental problems.

DESCRIPTION OF SYMBOLS 1 Contamination component diffusion prevention structure 2 Embankment 2a Embankment bottom part 2b Embankment upper part 3 Water stop material 4 Horizontal drain 5 1st adsorption layer 6 2nd adsorption layer 7 Water-impervious material 8 Coarse grain layer 9 Embankment 10 Covering layer 11 Adsorber 11a Adsorbent 20 Experimental tank 21 Soil tank 21a, 21b Dividing plate 22a, 22b, 22c, 29 Drain pipe 23, 25 Standard sand layer 24 Contaminated soil layer 26 Bean gravel layer 27 Adsorption layer 28 Non-permeable material
30 Artificial rainfall device
31 housing
31a side wall
31b Top plate
32 Humidifier
33 mesh
33a Needle-like protrusion
34 Supersaturated chamber 40 Evaporation experiment device 41 Experimental tank 41a Dividing wall 42 Drain drain 43 Drain pipe 44 Standard sand layer 45 Contaminated soil 46 Adsorbed layer 47 Halogen heater 48 Reflector plate 49 Water supply tank 49a Water supply pipe 49b Overflow pipe 50 External water supply tank

Claims (3)

A poorly permeable material disposed in the upper layer of the contaminated soil as having a moisture permeability while preventing water permeation,
A first adsorption layer that is buried in a lower layer of the contaminated soil and adsorbs a contaminant component contained in the hardly permeable material and the permeated water that has passed through the contaminated soil, and is buried between the hardly permeable material and the contaminated soil. And a second adsorbing layer on which the contaminating component contained in the contaminated soil is adsorbed .   The contamination component diffusion preventing structure according to claim 1, further comprising a coarse particle layer formed on an upper layer of the hardly water-permeable material. Embankment covering the contaminated soil;
A water stop material embedded in a lower layer of the first adsorption layer;
A horizontal drain having water absorption and embedded between the waterstop material and the first adsorption layer;
An adsorbing device that is disposed outside the embankment and through which permeated water that is guided to the horizontal drain and drained passes, and adsorbent that adsorbs contaminating components contained in the contaminated soil is exchangeably filled. The contamination component diffusion preventing structure according to claim 1, wherein the contamination component diffusion preventing structure is provided.