JP2003001212A - Method confining contaminated soil into ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for confining contaminated soil into ground which enables the effective reuse of the ground surface even after the contaminated soil is confined. SOLUTION: In this method for confining contaminated soil underground, the contaminated soil 11 is confined by surrounding the circumference of the contaminated soil 11 in the ground with an impervious wall 12, and providing a composite impervious layer 14 formed by heaping a barrier layer 14A made of a gravel layer 14a and a sand layer 14b, an impervious layer 14B made of bentonite-mixed soil and a drainage layer 14C made of a gravel layer on the upper part of the contaminated soil 11 and a surface layer 15 which is made of good quality soil covering the upper part of the composite impervious layer 14 and has a prescribed thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for containing contaminated soil in the ground, and more particularly to a method for containing land on the ground surface of a landfill.

[0002]

2. Description of the Related Art Conventionally, when there is contaminated soil in the ground, such as a site of a chemical factory, as shown in FIG. The impermeable wall 51 is provided, and the impermeable layer 52 is provided on the ground surface to prevent vertical diffusion, so that the contaminated soil 53 in the ground is prevented from diffusing pollutants into the surrounding environment. In detail,
The perimeter of the contaminated soil 53 is surrounded by the impermeable wall 51 whose lower end reaches the impermeable ground 54, and the impermeable sheet 55 is laid on the contaminated soil 53 in the impermeable wall 51 and is made of cohesive soil on it. The impermeable layer 52 is provided, and finally, the surface layer 56 is formed by embanking earth and sand on the impermeable layer 52. At this time, the shape of at least the ground surface 50 side of the water-impervious layer 52 is made to be a convex shape so as to facilitate drainage during rainfall. Therefore, generally, the shape of the ground surface is also a convex shape. Also,
Considering the rise of groundwater level of the ground due to rainfall, the impermeable wall 51 is usually positioned such that the upper end thereof is higher than the average groundwater level point and higher than the lower end of the impermeable layer 52. The surroundings of the contaminated soil 53 are completely isolated from the surrounding soil. Even when contaminated soil is buried in the ground and contained, measures to prevent the diffusion of pollutants into the surrounding environment are taken by the same method as above.

[0003]

However, it is difficult to construct a building by excavating a foundation or the like because of the structure in the above-mentioned conventional underground containment method. Moreover, since the shape of the ground surface is also convex, it is difficult to use it as a sports park, and the reuse of land has been considerably limited. Further, since the earth and sand of the surface layer 56 is generally only about several tens of cm, there is a risk of damaging the impermeable layer 52 when excavating when making a workpiece on the earth and sand surface. Further, although the cohesive soil forming the water-impervious layer 52 is excellent in water impermeability, it conversely promotes a capillarity phenomenon when it evaporates on the ground surface. Although it is installed, it has the opposite effect when the groundwater level is high, and the capillary rise causes pollutants in the lower part to rise near the ground surface 50,
The ground surface 50 may be contaminated. Furthermore, in the above-mentioned conventional structure, since groundwater is confined in the impermeable wall 51 and fluidity is lost, the quality of the confined groundwater deteriorates, and pollutants in the impermeable wall 51 increase. There was a possibility.

The present invention has been made in view of the conventional problems, and it is an object of the present invention to provide a method for containing contaminated soil in the ground, which enables effective reuse of the ground surface even after containing contaminants. To aim.

[0005]

A method for confining contaminated soil to the ground according to claim 1 of the present invention comprises an impermeable wall around a contaminated soil in the ground or a contaminated soil buried in the ground. On the upper part of the contaminated soil, a blocking layer made of sand or gravel, a water blocking layer containing cohesive soil, and a composite water blocking layer in which a drainage layer made of sand or gravel is sequentially deposited,
It is characterized in that a surface layer made of good quality soil having a predetermined depth is provided on the upper part of the composite impermeable layer.
Capillary rise of pollutants from the lower part of the composite impermeable layer can be prevented, so that the contaminated soil can be reliably contained in the ground. In addition, since the composite impermeable layer has a drainage layer,
There is no need to make the ground surface of the surface layer convex. Further, since the surface layer is formed at a predetermined depth such that at least land such as plants can be used in the living area, the ground surface can be effectively reused.

The method for confining contaminated soil in the ground according to claim 2 has the property of absorbing moisture and swelling as the above-mentioned cohesive soil in order to further ensure the water-shielding effect, and has a long-term water-shielding performance. It is characterized by using bentonite mixed soil that can be exerted over a period of time.

The method for confining contaminated soil in the ground according to claim 3, wherein the barrier layer is a gravel layer in contact with the contaminated soil,
It is characterized by comprising a sand layer provided between the gravel layer and the water-impervious layer, by which the gravel layer and the water-impervious layer can be reliably separated, and the contaminant It is possible to further improve the effect of preventing capillary rise.

The method for confining contaminated soil in the ground according to claim 4, wherein an opening is provided on the upper side of the impermeable wall at a position corresponding to the average groundwater level point of the surface layer, and drainage is caused by heavy rainfall. The feature is that it copes with the rise of the groundwater level beyond the function.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the underground confinement structure of contaminated soil according to the present embodiment. In FIG. 1, 11 is a contaminated soil in the ground, and 12 is a construction constructed by surrounding the contaminated soil 11 with a steel sheet pile. Was done,
An impervious wall whose lower end reaches the impermeable ground 13, an impervious layer 14A composed of a gravel layer 14a and a sand layer 14b, an impervious layer 14B composed of bentonite mixed soil, and a drainage layer 14C composed of a gravel layer. , A composite impervious layer formed by sequentially depositing on the contaminated soil 11, a surface layer 15 made of good quality soil such as earth and sand formed on the upper part of the complex impervious layer 14, and 16 confining the contaminated soil. It is a foundation pile for standing the building 17 on the ground. In addition, in the upper part of the above-mentioned impermeable wall 12,
A drainage opening 12s communicating with the surrounding soil 20 is provided at a position (close to the ground surface) higher than the average groundwater level located in the surface layer 15.

Next, a method of confining contaminated soil in the ground according to the present invention will be described. According to this method, a special water-impervious layer (composite water-impervious layer 14) as described below is provided in the ground 1.5 to 2.0 m from the ground surface 10, which is generally considered to be a living area. By providing the surface layer 15 made of high-quality soil on the water shield layer 14, the restriction of land use on the ground surface 10 is relaxed. First, in order to prevent the contaminated soil 11 from spreading in the horizontal direction, a steel sheet pile is disposed so as to surround the contaminated soil 11 and the impermeable wall 1 is provided.
Build 2. At this time, the lower end of the impermeable wall 12 reaches the impermeable ground 13, and the upper end of the impermeable wall 12 is the ground surface 1.
Extend to near 0. Next, the soil above the contaminated soil 11 is excavated from the ground surface for about 2.5 m, and the remaining soil is carried out. First, a gravel layer 14a having a thickness of about 15 cm is provided,
A sand layer 14b having a thickness of about 5 cm is provided on the barrier layer 1
4A is formed, and a thickness of 50 cm is formed on the barrier layer 14A.
A water-impervious layer 14B made of bentonite mixed soil is formed, and further, a water-impervious layer 14 having a multi-layer structure is formed on the water-impervious layer 14B by depositing a drainage layer 14C having a thickness of about 10 cm. Then, finally, a surface layer 15 made of good quality soil is provided on the composite impermeable layer 14. In this example, the surface layer 15 has a thickness of about 1.8 m. In addition, when the building 17 is planned to stand on the ground surface 10, the foundation pile 16 is built in the ground before the formation of the composite impermeable layer 14. The foundation pile 16 may be constructed after the underground containment is completed.

As described above, the composite impermeable layer 14 of the present invention is made of cohesive soil (bentonite mixed soil).
A barrier layer 1 composed of a gravel layer 14a and a sand layer 14b under B
4A, the capillary rise of pollutants from the contaminated soil 11 under the composite impermeable layer 14 is blocked by the gravel layer 14a as shown in FIG. Therefore, since the pollutant does not reach the water-impervious layer 14B, the pollutant does not reach the ground surface 10 even when the groundwater level is high.
It is possible to prevent the ground surface 10 from being contaminated by rising to the vicinity. The sand layer 14b provided above the gravel layer 14a also has a function of suppressing capillary rise, but here, it is prevented that the gravel forming the gravel layer 14a gets into the cohesive soil of the water blocking layer 14B. Thus, it plays a role of separating the gravel layer 14a and the water blocking layer 14B. Further, the composite water-impervious layer 14 of the present invention is a drainage layer 1 comprising a gravel layer having excellent water permeability on the water-impervious layer 14B.
Since it has 4C, it prevents rain seepage water from permeating into the contaminated soil 11 at the bottom by the impermeable layer 14B, and the rain seepage water from the drainage layer 14C by using, for example, a pipe, etc. Can be discharged to the Therefore, the rainfall permeated water can be surely discharged, and the water shielding effect can be improved. Further, since it is easy to drain water when it rains, it is not necessary to form the ground surface 10 into a convex shape, which has an advantage that the land can be effectively used.

In this example, bentonite mixed soil is used as the cohesive soil forming the water shield layer 14B in order to further ensure the water shield effect. Since this bentonite mixed soil has a property of absorbing water and swelling, it is not only superior in water impermeability to general clay, but also contains a large amount of sand and is therefore less likely to be deformed than clay. Also, since there is no cracking due to deformation of the ground like cement,
The water-blocking performance can be exhibited for a long period of time. Furthermore,
Even when the foundation pile 16 is constructed by using the bentonite mixed soil, the bentonite mixed soil is deformed under the load of the surface layer 15 having a thickness of about 1.8 m, and a gap around the foundation pile 16 is formed. Foundation pile 16
It has an advantage that the water impermeability is not impaired by hitting.

Further, since the drainage opening 12s communicating with the surrounding soil 20 is provided above the impermeable wall 12, groundwater near the ground surface 10 can always flow, and the deterioration of water quality can be prevented. Not only that, but also when there is an excessive rise in the groundwater level beyond the drainage function such as a heavy rain, drainage from the opening 12s prevents the groundwater surface from reaching the vicinity of the ground surface 10. can do. Furthermore, in this example, since the surface layer 15 made of good quality soil having a thickness of about 1.8 m is provided between the composite impermeable layer 14 and the ground surface 10, even if the ground surface 10 is slightly excavated, Water layer 14
Not only will the building be damaged, but also if a deep basement is not created from the ground surface 10, the building 17 can be erected sufficiently, and the restrictions on land use can be greatly relaxed.

As described above, in the present embodiment, the perimeter of the contaminated soil 11 in the ground is surrounded by the impermeable wall 12, and the barrier layer 14A composed of the gravel layer 14a and the sand layer 14b is provided above the contaminated soil 11. Impermeable layer 1 consisting of bentonite mixed soil
4B and a drainage layer 14C composed of a gravel layer, the contaminated soil 11
And a composite impermeable layer 14 formed by being sequentially deposited on the upper part of the, to prevent capillary rise of pollutants by the impervious layer 14A, and by the drainage layer 14C and impermeable layer 14B,
Since the contaminated soil 11 is sealed with water so that the contaminated soil 11 is contained, the diffusion of the pollutants can be surely prevented. Further, since the surface layer 15 made of good quality soil having a predetermined thickness is provided so as to cover the upper part of the composite impermeable layer 14, the ground surface 10 can be effectively used.

In the above embodiment, the blocking layer 14A is used.
Is composed of the gravel layer 14a and the sand layer 14b, but the same effect can be obtained even with a gravel layer in which sand and gravel are mixed in an appropriate composition. In addition, the impermeable layer 14B and the drainage layer 14C
A sand layer may be provided between the drainage layer and the drainage layer to reliably separate the drainage layer 14C and the water shield layer 14B. Moreover, the gravel layer 14a, the sand layer 14b (blocking layer 14A), the water blocking layer 14B of this example,
The thicknesses of the drainage layer 14C and the surface layer 15 are not limited to the above examples, but the soil and groundwater level of the ground,
It is appropriately determined depending on the property and scale of the contaminated soil 11. Further, in the above example, the method of confining the contaminated soil 11 in the ground has been described. However, when the contaminated soil is newly buried in the ground, the contaminated soil is contained by the same method as described above, so that the pollutant is removed. The ground surface can be effectively reused even after containment.

[0016]

As described above, according to the present invention,
An impermeable wall is provided around the contaminated soil in the ground or the contaminated soil buried in the ground, and a shielding layer made of sand or gravel and an impermeable layer containing cohesive soil are provided on the contaminated soil. A composite impermeable layer is formed by sequentially depositing a drainage layer made of sand or gravel, and a surface layer made of good quality soil is provided to cover the upper part of the composite impermeable layer with a predetermined depth to contain the contaminated soil. As a result, it is possible to reliably prevent the capillary rise of pollutants from the lower part of the composite impermeable layer and to effectively reuse the ground surface. Further, by using bentonite mixed soil as the above-mentioned cohesive soil, the water blocking effect can be retained more reliably and for a long time.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an underground confinement structure of contaminated soil according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a method for confining contaminated soil in the ground according to the present embodiment.

FIG. 3 is a schematic diagram showing a conventional underground containment structure for contaminated soil.

[Explanation of symbols]

10 ground surface, 11 contaminated soil, 12 impermeable walls, 12s
Opening for drainage, 13 impermeable ground, 14 composite water blocking layer, 14A blocking layer, 14a gravel layer, 14b sand layer,
14B water impermeable layer, 14C drainage layer, 15 surface layer, 16
Foundation piles, 17 buildings, 20 soil around.

Claims (4)

[Claims] 1. An impermeable wall around a contaminated soil in the ground or a contaminated soil buried in the ground, a barrier layer made of sand or gravel above the contaminated soil, and a water barrier containing cohesive soil. Layer and a drainage layer composed of sand or gravel are sequentially deposited, and a surface layer made of good quality soil having a predetermined depth is provided on top of the composite barrier layer. The method of containing contaminated soil in the ground. 2. The method for containing contaminated soil in the ground according to claim 1, wherein bentonite mixed soil is used as the cohesive soil. 3. The barrier layer is composed of a gravel layer in contact with the contaminated soil and a sand layer provided between the gravel layer and the water barrier layer. Two
The method of containing contaminated soil in the ground as described in. 4. The pollution according to any one of claims 1 to 3, wherein an opening is provided on an upper side of the impermeable wall at a position corresponding to an average groundwater level point of the surface layer. How to contain soil underground.