JP2011056430A - Surplus soil disposal structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a surplus soil disposal structure which can be employed without limit of physiographic form and can efficiently neutralize acidic water bleeding out of drilling debris. <P>SOLUTION: The surplus soil disposal structure 1 comprises a drilling surplus soil layer 2, a neutralization layer 3 which covers the side faces and bottom face of the drilling surplus soil layer 2 to neutralize acidic water bleeding out of the drilling surplus soil layer 2, and a soil covering layer 4 which covers the upper face of the drilling surplus soil layer 2 to limit the amount of penetrating water, and the neutralization layer 3 contains a neutralizing material containing calcium carbonate as a main component and is made so thick as to keep a needed stagnation time for neutralizing the acidic water and prevent the acidic water from bleeding outside. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a remaining soil disposal structure.

  In the disposal of residual soil such as excavations containing pyrite, etc., it is necessary to take measures to prevent acid water generated by oxidative dissolution from leaching to the surrounding ground.

Conventionally, when excavation shears containing pyrite are disposed of, it is common to add and neutralize neutralizing materials such as slaked lime and bury them in a disposal site.
However, adding a large amount of slaked lime may cause alkali contamination, so it was necessary to carry out after careful examination of the relationship between the contamination concentration of excavation shear and the mixing amount, which required time and effort. .

  On the other hand, Patent Document 1 discloses a residual soil disposal structure in which an underground wall containing an alkaline material is formed so as to intersect an inclined upper end and an inclined lower end in an inclined direction in an embankment stacked on an inclined ground.

JP 9-220579 A

However, the conventional residual soil disposal structure cannot be employed depending on the topography of the residual soil disposal site because it can be employed only on sloped ground.
In addition, if infiltrated water that exceeds the capacity of the underground wall flows, contaminated water may flow out to the surrounding ground.

  Therefore, it is an object of the present invention to propose a residual soil disposal structure that can be employed without being limited to the topographic shape and that can effectively neutralize acidic water that exudes from excavation. To do.

  In order to solve the above-mentioned problems, the present invention provides an excavation residual soil layer, a neutralization layer that covers a side surface and a bottom surface of the excavation residual soil layer, and neutralizes acidic water that exudes from the excavation residual soil layer, and the excavation residual soil layer A residual soil disposal structure comprising a soil covering layer that covers the upper surface of the soil and restricts the amount of water that penetrates, and the neutralizing layer is made of a neutralizing material mainly composed of calcium carbonate, and neutralizes the acidic water Therefore, it has a layer thickness that ensures a necessary residence time and prevents the acidic water from leaching to the outside.

  The layer thickness of the neutralization layer is preferably not less than a value obtained by dividing the product of the flow rate of the permeated water of the neutralization layer and the residence time necessary for the neutralization by the porosity of the neutralization layer. .

In such a residual soil disposal structure, acidic water generated in the excavated residual soil layer is neutralized by the neutralization layer, so that the contaminated water is prevented from leaching to the outside. Since the neutralization layer is formed to have a thickness that can secure the reaction time necessary for neutralizing the acidic water, it can be neutralized effectively.
Here, for example, limestone or dolomite is used as the neutralizing material mainly composed of calcium carbonate.

  In addition, the construction is easy due to the simple structure of simply covering the periphery of the excavated soil layer with a neutralization layer.

  In addition, the amount of water penetrating from the outside into the excavated residual soil layer is limited by the cover soil layer, so that the water penetration into the excavated residual soil layer can be equalized, and the neutralization layer thickness can be set to the minimum necessary It becomes. In addition, it is desirable to use a material that does not contain harmful substances and does not acidify the soil covering layer.

  In the residual soil disposal structure, if the water permeability coefficient of the neutralization layer is greater than or equal to the excavation residual soil layer, and the hydraulic conductivity coefficient of the excavation residual soil layer is set to be greater than or equal to the cover soil layer, the permeated water is in each layer. It is possible to prevent water from being drowned at the boundary portion.

  According to the present invention, it is possible to construct a residual soil disposal structure that can be adopted without being limited to topographic shapes and that can effectively neutralize acidic water that exudes from excavation. Become.

It is sectional drawing which shows the outline | summary of the remaining soil disposal structure which concerns on suitable embodiment of this invention. It is sectional drawing which shows the modification of a remaining soil disposal structure. It is sectional drawing which shows the other modification of the remaining soil disposal structure. It is sectional drawing which shows the other modification of the remaining soil disposal structure. It is sectional drawing which shows the other modification of the remaining soil disposal structure. (A) is a schematic diagram which shows the column used by the laboratory test, (b) is a graph which shows the examination result of the minimum layer thickness of a limestone layer.

Hereinafter, preferred embodiments of the present invention will be described.
The remaining soil disposal structure 1 according to the present embodiment is a structure for embedding disposal of excavation shears in a recess (groove or the like) formed in the ground 5, as shown in FIG. A limestone layer (neutralization layer) 3 covering the side surface and bottom surface of the remaining soil layer 2 and a covering soil layer 4 covering the upper surface of the excavated residual soil layer 2 and the limestone layer 3 are configured.

  The excavation residual soil layer 2 is formed by excavation shear embedded in a recess formed in the ground 5. In the present embodiment, excavation shear containing pyrite is disposed.

  The excavated residual soil layer 2 is formed by burying excavated ladle in a recess in which the limestone layer 3 is laid with a predetermined thickness.

The limestone layer 3 is a neutralization layer formed so as to cover the side surface and the bottom surface of the excavated residual soil layer 2.
The limestone layer 3 is a layer provided to prevent permeated water that has permeated into the excavated residual soil layer 2 due to rainfall or the like from seeping out into the surrounding ground (ground 5) in a state of containing contaminants.
In this embodiment, limestone is used as the neutralizing material. However, the neutralizing material is not limited to limestone as long as it is a material mainly composed of calcium carbonate. For example, dolomite may be used. .

When water permeates into the excavated soil layer 2, sulfuric acid acidic water is generated by oxidizing and dissolving pyrite in the excavated shear. The limestone layer 3 neutralizes the sulfuric acid acidic water oozed from the excavated residual soil layer 2 with calcium carbonate of limestone.
In this embodiment, the particle size of the limestone that constitutes the limestone layer 3 is set so that the permeability coefficient of the limestone layer 3 is equal to or greater than the permeability coefficient of the excavation residual soil layer 2. In addition, the kind of limestone used in the limestone layer 3 is not limited, and selects and uses it suitably.

  The layer thickness of the limestone layer 3 is set to a thickness that can secure the reaction time (retention time) necessary for neutralizing the sulfuric acid acidic water.

The thickness H of the limestone layer 3, first, calculates the estimated layer thickness H _SA, set by selecting whichever is larger which was compared with the minimum layer thickness H _SB. Incidentally, the lowest layer thickness _{H SB} is limestone constituting the limestone layer 3 particle size is of less than 4.75 or more 9.5 mm 4.5 cm or more, the particle size of limestone is less than 0.25 4.75mm In this case, the length is 2 cm or more. Here, the particle size of the limestone may be determined based on the result of the sieve test (JISA-1204).

The calculated layer thickness _HSA is calculated by calculating the product of the flow rate S of the osmotic water in the limestone layer 3 calculated by the hydraulic conductivity k of the limestone layer 3 and the residence time T necessary for neutralization of the acidic sulfuric acid water. It is calculated by dividing by the porosity p of the layer 3 (see Equation 1).

H _SA = S × T / (p / 100) (1)
Where H _SA : Calculated layer thickness (cm)
S: Flow rate of osmotic water (cm / sec) = k × i
T: Residence time required for neutralization (sec)
p: Porosity of limestone layer (%)
k: Permeability coefficient (cm / sec)
i: Hydrodynamic gradient

  The limestone layer 3 is laid on the surface of the recess formed in the ground 5 in a state where the layer thickness H is secured before the excavation shear is introduced.

  The soil covering layer 4 is a layer formed so as to cover the upper surface of the excavated residual soil layer 2 in order to prevent the residual excavated soil layer 2 from flowing out due to wind and rain.

  The material constituting the soil covering layer 4 is not limited as long as it does not contain harmful substances and does not acidify, and may be formed by appropriately selecting the material. The layer thickness of the soil covering layer 4 is not limited and can be set as appropriate. In this embodiment, the material which comprises the soil covering layer 4 is selected so that the water permeability coefficient of the soil covering layer 4 may become smaller than the water permeability coefficient of the excavation residual soil layer 2.

  In the present embodiment, the soil covering layer 4 is formed so as to cover the upper surface of the excavated residual soil layer 2 and the upper surface of the limestone layer 3. Note that the cover layer 4 only needs to be formed so as to cover at least the surface (upper surface) of the excavated residual soil layer 2, and does not necessarily need to cover the surface of the limestone layer 3.

  As mentioned above, according to the residual soil disposal structure 1 of this embodiment, since it is a simple structure which only forms the limestone layer 3 around excavation shear, the site for installing facilities, such as a neutralization plant, and the said facilities is secured. There is no need to do this, and it is possible to construct the apparatus simply and inexpensively.

  Moreover, since the layer thickness of the limestone layer 3 covering the periphery of the excavated residual soil layer 2 is ensured to be 2 cm or more, the sulfuric acid acidic water generated by oxidizing and dissolving the pyrite contained in the excavated residual soil layer 2 is neutralized. It is possible to prevent the exudation of contaminants to the surrounding ground.

  Moreover, since limestone is used, even if it dissolves in water, the pH only rises by about 8.5, so it is less likely to cause alkali contamination.

  In addition, since the permeability coefficient of the limestone layer 3 is greater than or equal to the excavation residual soil layer 2 and the hydraulic conductivity coefficient of the excavation residual soil layer 2 is greater than or equal to the covering soil layer 4, It is prevented from flooding. Therefore, flooding occurs at the boundary between the excavation residual soil layer 2 and the cover soil layer 4 and the cover soil flows out, or flooding at the boundary between the excavation residual soil layer 2 and the limestone layer 3 forms a water channel. It is possible to prevent the water from leaching to the ground 5 without being neutralized.

  Moreover, since the surface of the excavation residual soil layer 2 is covered with the covering soil layer 4, the amount of water (rainfall, etc.) penetrating into the excavation residual soil layer 2 is adjusted and water infiltration is equalized. Thereby, the quantity and density | concentration of sulfuric acid acidic water produced | generated in the excavation residual soil layer 2 are equalized, and the neutralization efficiency by the limestone layer 3 is improved more.

In addition, the structure of the remaining soil disposal structure 1 is not limited, It can form suitably according to the topography etc. of the ground 5.
For example, when excavating the excavation shear on the flat ground 5, the excavated residual soil layer 2, and the limestone layer 3 covering the side and bottom surfaces of the excavated residual soil layer 2, as in the residual soil disposal structure 1 a shown in FIG. The excavation residual soil layer 2 and the cover soil layer 4 covering the surface of the limestone layer 3 are configured.

The remaining soil disposal structure 1a is formed by the following procedure. First, the excavated residual soil layer 2 is embanked in a trapezoidal cross section with a stable gradient secured on the upper surface of the limestone layer 3 laid on the ground 5 with a thickness of 2 cm or more secured. Next, the limestone layer 3 is formed in a state where a thickness of 2 cm or more is secured so as to cover the side surface of the excavated residual soil layer 2. Further, the cover soil layer 4 is formed so as to cover the upper surface of the excavated residual soil layer 2 and the upper surface and side surfaces of the limestone layer 3.
Note that the soil cover layer 4 only needs to be formed so as to cover at least the surface (upper surface) of the excavated residual soil layer 2, and does not necessarily need to cover the surface of the limestone layer 3. In order to prevent flooding between the limestone layer 3 and the ground 5, a drain pipe penetrating the cover soil layer 4 from the lower end of the limestone layer 3 may be provided.

  Moreover, like the residual soil disposal structure 1b shown in FIG. 3 or the residual soil disposal structure 1c shown in FIG. 4, a soil layer 6 having a smaller hydraulic conductivity than the limestone layer 3 is formed between the limestone layer 3 and the ground 5. Therefore, the residence time of the permeated water in the limestone layer 3 may be increased.

According to the remaining soil disposal structures 1b and 1c, even if the particle size of the limestone constituting the limestone layer 3 is increased, a desired residence time can be secured, so that the sulfuric acid acid water leached from the excavated residual soil layer 2 is neutralized. Can do.
Here, it is desirable that the material constituting the clay layer 6 is made of a material having finer grains than the ground 5. Note that the same material as that of the soil covering layer 4 may be used as the material constituting the covering layer 6.

  Moreover, when the ground 5 is inclined, the remaining soil disposal structure 1d may be formed by embankment along an inclined surface (slope).

  When the remaining soil disposal structure 1d is formed along the slope, the limestone layer 3b is formed along the slope, and the excavated residual soil layer 2 is formed on the limestone layer 3b while ensuring a stable gradient. And the side surface (slope) of the excavation residual soil layer 2 is covered with the limestone layer 3a. Furthermore, the surface of the excavation residual soil layer 2 and the limestone layer 3 (3a, 3b) is covered with the covering soil layer 4.

  In the residual soil disposal structure 1d, the sulfuric acid acidic water may be guided to the limestone layer 3a by piping the drain pipes 7 and 7 across the excavated residual soil layer 2 and the limestone layer 3a. At this time, since the sulfuric acid acid water that has permeated into the limestone layer 3a can flow along the slope of the limestone layer 3a to ensure a sufficient residence time, the limestone used for the limestone layer 3a has the other particle size. The particle size of the limestone used in the limestone layer 3b may be larger.

  In addition, the drainage port 8 is formed in the lowest part of the residual soil disposal structure 1d with a material with a large hydraulic conductivity so that drainage from the limestone layer 3 is possible. The drain port 8 may be provided with limestone or a drain pipe.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

Next, the Example which concerns on the setting method of the layer thickness of a limestone layer is shown.
In the present embodiment, the indoor test using a column 10, was investigated lowest layer thickness H _SB limestone layer.

  In this test, as shown in FIG. 6A, a 0.01 mol / L sulfuric acid aqueous solution 12 was flowed from the lower part into the column 10 into which the limestone 11 was introduced, and the limestone 11 in the column 10 was passed through. Then, the neutralization characteristic by a limestone layer was measured by measuring pH of the aqueous solution 13 discharged | emitted from the upper part.

  In this test, the particle size of limestone is 4.75 to 9.5 mm (case 1), the particle size is 2.0 to 4.75 mm (case 2), and the particle size is 0.25 to 2.0 mm. Less than (case 3) were measured (see Table 1).

The minimum neutralization ability was defined as the ability to neutralize acidic water to at least pH 5.8 so as to satisfy the water pollution prevention method drainage standard.
Since limestone is consumed as the neutralization reaction proceeds, the limestone height in the column decreases with the progress of the neutralization reaction.

In this test, without replenishing the limestone in the column 10, the height of the limestone 11 is changed in a decreasing direction, and the sulfuric acid aqueous solution 12 is caused to flow into the column 10 (limestone 11) at a constant flow rate to adjust the pH. The neutralization effect of was measured. According to this test, the point at which the necessary neutralization reaction does not occur when the limestone height exceeds a predetermined value becomes clear.
The result of this test is shown in FIG. Here, in the drawings, reference numerals C1, C2, and C3 indicate case 1, case 2, and case 3, respectively.

As shown in FIG. 6B, in case 1 (C1), when the height (layer thickness) of the limestone is 4.5 cm or less, the pH is lowered and the neutralization effect does not satisfy the above minimum standard. It was. In case 2 (C2) and case 3 (C3), when the height (layer thickness) of limestone was 2 cm or less, the pH value increased and decreased, and the neutralization effect became unstable. Therefore, the lowest layer thickness _{H SB} limestone layer, if the particle size of the limestone 11 is less than 4.75 or more 9.5 mm 4.5 cm, when the particle diameter of the limestone 11 is less than 0.25 or more 4.75mm It was demonstrated that the thickness of the limestone layer 3 should be 2 cm or more.

1 Waste soil disposal structure 2 Excavated soil layer 3 Limestone layer 4 Covering layer 5 Ground 6 Soil layer 7 Drain pipe 8 Drain port

Claims (3)

The excavated residual soil layer, the neutralization layer that covers the side and bottom surfaces of the excavated residual soil layer and neutralizes the acid water that exudes from the excavated residual soil layer, and the covered soil layer that covers the upper surface of the excavated residual soil layer and limits the amount of water that penetrates A residual soil disposal structure comprising:
The neutralization layer is composed of a neutralizing material mainly composed of calcium carbonate, and has a layer thickness that ensures the residence time necessary to neutralize the acidic water and prevents the acidic water from leaching to the outside. The remaining soil disposal structure is characterized by that.   The layer thickness of the neutralization layer is not less than a value obtained by dividing the product of the flow rate of permeated water of the neutralization layer and the residence time required for neutralization by the porosity of the neutralization layer, The residual soil disposal structure according to claim 1.   The magnitude of the hydraulic conductivity of the neutralization layer is greater than or equal to the excavated residual soil layer, and the magnitude of the hydraulic conductivity of the excavated residual soil layer is greater than or equal to the covered soil layer. The remaining soil disposal structure described in 1.

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