JP5743449B2 - Treatment structure with water flow structure in contaminated soil treatment and its construction method - Google Patents

Description

The present invention relates to a treatment structure having a water flow structure and a construction method therefor so as not to hinder the flow of groundwater in the treatment of contaminated soil where a groundwater area exists.

The main causative substances of soil contamination are volatile organic substances, heavy metals, agricultural chemicals, etc., so the soil pollution countermeasures law categorizes hazardous substances as type 1 (volatile organic substances), type 2 (heavy metals, etc.), type 3 It is classified into species (agricultural chemicals, etc.), and the elution volume standard and the second elution volume standard are established. As for the second elution amount standard for heavy metals and the like (second type), a standard 10 to 30 times the elution amount standard is set according to the metal type. When performing pollution countermeasures, contaminated soil that exceeds the second elution amount standard is insolubilized and adapted to the second elution amount standard, and contaminated soil that exceeds the elution amount standard is insolubilized and the elution amount standard It is necessary to take measures against pollution after adapting to the above.

Treatment measures such as solidification / insolubilization, in-situ containment, and imperviousness containment are performed as countermeasures for contaminated soil. Solidification / insolubilization treatment includes in-situ insolubilization measures and insolubilization backfilling measures. In-situ insolubilization measures do not excavate contaminated soil, but inject solubilizing agents to prevent toxic substances from eluting, and it is necessary to make the soil less than the elution standard. The insolubilization backfilling process is a process of digging up contaminated soil, insolubilizing it, and backfilling it in situ.

In-situ containment surrounds contaminated soil with a water-blocking structure to prevent groundwater from flowing out of the area. There must be an impermeable layer in the lower part of the contaminated soil, the surface is paved with concrete or asphalt, groundwater observation wells are installed, groundwater does not rise, and groundwater standards are met Check regularly. Contaminated soil that exceeds the second elution amount standard is constructed after injecting an insolubilizing agent or the like to prevent toxic substances from eluting. Japanese Patent Application Laid-Open No. 2007-61799 (Patent Document 1) describes an in-situ containment method including a pH adjusting means for groundwater.

Containment of impermeable works involves excavating contaminated soil, forming a water-impervious layer or impervious work with double impermeable sheets at the excavation site, and then refilling the contaminated soil. At this time, the contaminated soil exceeding the second elution amount standard is insolubilized and reduced to the second elution amount standard or less, and then backfilled. Next, paving the surface with concrete or asphalt and installing a groundwater observation well, periodically confirming that there is no groundwater rise and that it meets groundwater standards.

JP 2007-61799 A

When the contaminated soil in the groundwater area is solidified and insolubilized, the treated body has extremely low water permeability and it becomes difficult for the groundwater to flow. Therefore, it is necessary to take measures to preserve the flow of the groundwater. Even in the case of in-situ containment and impermeable containment measures, the contaminated soil treatment area is sealed by the impervious works and the impermeable layer. It is necessary to take measures that do not interfere with this. In general, impermeable containment has a larger cross-section that hinders groundwater flow than in-situ containment, so there is a high need to ensure groundwater flow.

The present invention provides a treatment method and a treatment structure thereof that do not impede the flow of groundwater in the treatment of contaminated soil where a groundwater area exists.

The present invention relates to a water-permeable treatment method and a treatment structure in the following contaminated soil treatment.
[1] A water pipe is installed through the insolubilized body of the contaminated soil or at the lower part of the insolubilized body, the inside of the water pipe is filled with porous concrete, and both ends of the water pipe are insolubilized. A contaminated soil treatment structure characterized in that it opens to a groundwater area outside the treatment body and allows groundwater to pass through porous concrete inside the water pipe.
[2] The contaminated soil treatment structure according to [1], wherein a vertical hole is connected to a pipe end of the water pipe, and the vertical hole extends to the ground surface and also serves as an observation well.
[3] A vertical hole is connected to the pipe end on the upstream side of the groundwater so that a space is formed in front of the pipe end, and the groundwater area side of the vertical hole is formed on a permeable wall. The contaminated soil treatment structure according to the above [2], wherein a water permeable filter is replaceably installed in a pipe end opening of the water pipe .
[4] Excavate contaminated soil, mix with insolubilizing material, insolubilize, install a water pipe at the excavation site, and place and fill with porous concrete inside the water pipe, or porous inside A water pipe filled with concrete is installed in the excavation trace, and then the insolubilized body of contaminated soil is backfilled in the excavation trace, and both ends of the water pipe are opened to the groundwater area outside the insolubilized body. A method for treating contaminated soil, characterized by forming a structure through which groundwater can be passed through porous concrete inside a water pipe by a construction method for forming and providing a surface layer.
[5] After installing the water pipe in the excavation trace, the vertical hole communicating with the pipe end opening is installed, and then the insolubilized treated body of the contaminated soil is backfilled to form the treatment structure having the vertical hole. [4] A method for treating contaminated soil according to [4].

According to the contaminated soil treatment structure and the treatment method of the present invention, since a water pipe that allows groundwater to flow through porous concrete inside the pipe is provided, the flow of groundwater is blocked even in a soil-contaminated area of the groundwater area. Can take anti-pollution measures.

Since the water pipe used for the contaminated soil treatment of the present invention is filled with porous concrete inside the pipe, it has good water permeability and sufficient strength, and serves as a foundation for supporting the load on top. A water flow structure can be formed.

Schematic sectional view of a processing structure according to the present invention Partial explanatory diagram of processing structure Construction process diagram Implementation model diagram

Hereinafter, the present invention will be specifically described based on embodiments.
[Contaminated soil treatment body with water flow structure]
A schematic cross-sectional view of a contaminated soil treatment structure according to the present invention is shown in FIG. As shown in the drawing, in the contaminated soil treatment structure of the present invention, a water pipe 11 is installed below the insolubilized treated body 10 of the contaminated soil. The insolubilized body 10 is obtained by mixing an insolubilizing material in a contaminated soil and solidifying it to limit the amount of elution of heavy metals or the like to the second elution amount standard or less, or to the elution amount standard or less. The upper surface of the insolubilized body 10 is covered with a water shielding layer 12. The water shielding layer 12 is formed of concrete, asphalt, or the like.

The illustrated structure is an example of insolubilization or insolubilization backfilling in situ, and the insolubilized body 10 is formed on the upper side of the hardly water-permeable layer 13. The water conduit 11 is installed between the insolubilized body 10 and the hardly water-permeable layer 13. Similarly, in the in-situ containment measure, the water pipe 11 may be installed between the insolubilized body 10 and the hardly water-permeable layer 13. In the impermeable containment measure or the like, the water conduit 11 may be installed between a water shielding work (not shown) surrounding the backfilled insolubilized body and the insolubilized body.

The water pipe 11 may be made of concrete or made of polyvinyl chloride. The inside of the water flow pipe 11 is filled with porous concrete 16. After the water pipe 11 is installed, the porous concrete 16 may be filled into the water pipe, or the water pipe 11 previously filled with the porous concrete 16 may be used. Porous concrete 16 is a porous concrete in which the unit fine aggregate amount of concrete is greatly reduced, and has a large void (for example, a porosity of 15 to 40%), good water permeability and sufficient strength. (For example, compressive strength 16-30 N / mm ² ).

Water pipes with hollow interiors may be damaged due to insufficient strength when buried in the ground, but water pipes filled with porous concrete have sufficient strength, so when buried in the ground It can be used as a foundation for supporting an overload received from an insolubilized body, and a strong water flow structure can be formed. Moreover, if porous concrete is directly laid without using a water pipe, when groundwater flows, it will diffuse to the periphery and the flow will not be stable. By using a water pipe filled with porous concrete, groundwater can flow stably without diffusing.

A plurality of water pipes 11 can be installed according to the size of the insolubilized body 10. Both side pipe ends 14 of the water flow pipe 11 are opened toward the groundwater area 15 outside the insolubilized body 10. In the in-situ containment measure and the impermeable containment measure, etc., the both-side pipe ends 14 of the water flow pipe 11 are formed so as to penetrate the impermeable work (not shown) and extend to the groundwater area 15.

A vertical hole 17 is connected to at least one pipe end of the water flow pipe 11, and the vertical hole 17 extends to the ground surface and also serves as an observation well. Preferably, the vertical hole 17 is installed at the upstream pipe end of the groundwater or at both pipe ends. The water level and quality of groundwater can be observed through the vertical hole 17.

For example, as shown in FIG. 2, the vertical hole 17 is formed so that a space 18 is formed in front of the pipe end 14 of the water flow pipe 11, and the groundwater area side is a water-permeable wall 19. It is better to be able to observe the groundwater level.

Preferably, a water permeable filter 20 is installed in the pipe end opening on the upstream side of the ground water of the water pipe 11 in a replaceable manner. It is preferable that the upright hole 17 is formed in a size that allows an operator to enter and exit so that the operator can replace the filter 20 appropriately. By providing the water-permeable filter 20 and replacing it appropriately, clogging of the pipe end opening of the water pipe can be eliminated.

[Construction method]
The construction method of the contaminated soil processing structure which has the water flow structure which concerns on this invention is demonstrated below.
This construction method has, for example, the following steps (I) to (V). An outline of the processing steps is shown in FIG.

(I) Excavate contaminated soil to the surface.
(II) Solidify or insolubilize the excavated contaminated soil and insolubilize it.
For contaminated soil in which the elution amount of heavy metals etc. exceeds the second elution amount standard, the elution amount of heavy metals etc. is made to be equal to or less than the second elution amount standard by insolubilization treatment so that it can be backfilled. For contaminated soil where the elution amount of heavy metals etc. exceeds the elution amount standard, the elution amount of heavy metals etc. is reduced below the elution amount standard by insolubilization treatment so that it can be backfilled.

(III) Install water pipes at the excavation site.
(1) Place and fill porous concrete inside the water pipe. Alternatively, a water pipe filled beforehand with porous concrete is installed in the excavation trace. Water pipes will be installed so as not to disturb the groundwater gradient. For example, since the average hydraulic gradient including lowland to mountainous area is 0.015, it is only necessary to install the water pipe while maintaining a slope suitable for this hydraulic gradient with respect to the flow of groundwater. A plurality of water pipes can be installed according to the size of the insolubilized body.
(2) The both ends of the water pipe are extended outward from the insolubilized body and formed in an open state toward the groundwater area. In-situ containment measures and impervious containment measures, etc., the both ends of the water pipe are extended through the impervious work and open toward the groundwater area.

(IV) A vertical hole is formed.
(1) A vertical hole is preferably formed. The vertical hole is formed at the pipe end on the upstream side of the groundwater, or at the pipe ends on both sides, and is formed to extend to the surface of the earth so that it also serves as an observation well. The vertical hole may be formed of sheet pile steel plate or concrete. The lower end of the vertical hole is formed so that a space is created in front of the pipe end of the water pipe, and the water permeable wall is used on the groundwater area side.
(2) Preferably, the vertical hole is formed in a size that allows an operator to enter and exit, and a water permeable filter is installed in the pipe end opening on the upstream side of the groundwater in a replaceable manner.

(V) Backfill the insolubilized body.
After the installation of the water pipe and the formation of the vertical holes, the insolubilized body that conforms to the second elution amount standard is backfilled, and the surface layer is provided. The surface layer (water shielding layer) may be formed of concrete or asphalt.

[Implementation model for insolubilization backfilling measures]
The implementation model is shown in FIG. The target ground is an aquifer from 1 to 5 m below ground and a hardly permeable layer from 5 m deep. The contaminated soil exists in the depth of 0.5 to 5 m, and the size of the insolubilized body is 4.5 m deep × 40 m wide × 50 m long. In general, the soil quality of soil with soil contamination is mostly viscous soil, where pollutants are difficult to move. However, since it is related to the groundwater flow structure, sandy soil with a large amount of groundwater flow is set.

An example of construction conditions is shown below.
Inhibition cross section of groundwater flow: 4 × 40m (A = 160m ² )
Hydrodynamic gradient of groundwater I: 0.015 (Refer to the manual for soil contamination countermeasures)
Soil quality of aquifer (ground): Permeability coefficient of sandy ground k: 1 × 10 ^-2 cm / sec
Groundwater flow velocity v: k × I = 10 ⁻² × 0.015 = 1.5 × 10 ⁻⁴ cm / sec = 0.13 m / day = 47 m / year

[Water pipe]
Porous concrete is filled inside the water pipe (concrete, PVC).
Properties of porous concrete: porosity 15-40%, compressive strength 16-30 N / mm ²
Filling with porous concrete: Either of the following (1) or (2) may be used.
(1) Method of placing at the site: Placing the raw concrete inside the water pipe at the construction site.
(2) Precast; As a precast product, fill the inside of the water pipe with raw concrete at the factory.

A treatment structure having a water flow structure shown in FIG. 1 was formed according to the following construction procedure.
Procedure 1: Excavate contaminated soil on the surface, mix with insolubilizing material and insolubilize.
Step 2: Install water pipes. Porous concrete is filled by either (1) or (2) above.
Step 3: Backfill the insolubilized soil (body) to the top of the water pipe and compact.
Step 4: Cover the surface.
If necessary, install a well for confirmation upstream, and attach a filter to the opening at the end of the water conduit so that it can be replaced. As the filter, a commercially available non-woven fabric filter (permeability coefficient of about 1 × 10 ⁻¹ cm / sec) for a PVC porous tube was used.

10-insolubilized treated body, 11-water pipe, 12-water-impervious layer, 13-hardly permeable layer, 14-end of pipe, 15-ground water area, 16-porous concrete, 17-standing hole, 18-space, 19-water-permeable Sex wall, 10-filter.

Claims (5)

Through the insolubilized body of the contaminated soil, a water pipe is installed at the bottom of the insolubilized body, the inside of the water pipe is filled with porous concrete, and both ends of the water pipe are from the insolubilized body. A contaminated soil treatment structure characterized by being open to the outer groundwater area and allowing groundwater to pass through porous concrete inside the water pipe. The contaminated soil treatment structure according to claim 1, wherein a vertical hole is connected to a pipe end of the water pipe, and the vertical hole extends to the ground surface and also serves as an observation well. A vertical hole is connected to the pipe end on the upstream side of the groundwater so that a space is formed in front of the pipe end, and the groundwater area side of the vertical hole is formed on a water-permeable wall. The contaminated soil treatment structure according to claim 2, wherein a water permeable filter is replaceably installed in a pipe end opening of the water pipe . Excavate contaminated soil, mix with insolubilizing material, insolubilize, install a water pipe at the excavation trace, and place and fill with porous concrete inside the water pipe, or pre-fill with porous concrete inside The drainage pipe is installed in the excavation trace, and then the insolubilized treatment body of the contaminated soil is backfilled in the excavation trace, and both ends of the drainage pipe are formed in a state opened to the groundwater area outside the insolubilization treatment body, A method for treating contaminated soil, characterized in that a structure that allows groundwater to flow through porous concrete inside a water pipe is formed by a construction method for providing a surface layer. 5. After installing the water pipe in the excavation trace, a vertical hole communicating with the pipe end opening is installed, and then the insolubilized treated body of the contaminated soil is backfilled to form a treatment structure having the vertical hole. To treat contaminated soil.

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