JP2004330097A - Method for freezing and removing polluted soil and underground frozen body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for freezing and removing polluted soil, for making block-shaped frozen soil by utilizing a freezing technique and sealing the volatilization of a harmful substance or the malodor of waste with ice to more reduce an environmental risk than before while enhancing the removal/feed-out efficiency of polluted soil. <P>SOLUTION: This method for freezing and removing polluted soil has a cooling pipe arranging process for arranging cooling pipes in polluted soil, in which a pollutant is present, so as to make the distances between the center parts of the cooling pipes equal, a cooling process for supplying a freezing medium to the cooling pipes to form discontinuous frozen soil comprising the surface part of non-frozen soil and the remainder of frozen soil around the cooling pipes, and a frozen soil removing process for taking out the frozen part of discontinuous frozen soil to the surface of the ground. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention reduces environmental risks during excavation and transportation by obtaining contaminated soil containing odorous waste and volatile harmful substances as columnar block frozen soil, and lifting and removing the frozen soil to the surface. How to do it.
[0002]
[Prior art]
When excavating and heating soil contaminated with harmful substances such as mercury compounds, dioxins, and benzene, or when removing foul-smelling waste and sludge sludge, etc. There are problems such as volatilization of waste and bad smell of waste. Conventionally, as a solution to this, for example, a tent is installed around the contaminated site at the time of excavation and work is performed inside it to prevent harmful substances from volatilizing to the surrounding area and stink of waste. I have. At the time of transportation, contaminated soil is sealed with a drum or the like and is currently carried out. At the time of such excavation or at the time of enclosing the drum can, the operator takes measures such as wearing a toxic gas mask or the like.
[0003]
On the other hand, there is known a method of arranging a large number of cooling pipes in the ground to freeze the ground. Further, Japanese Patent Application Laid-Open No. 11-169837 of Patent Document 1 discloses a method of purifying a contaminated ground in which, following a step of freezing the contaminated ground area, gas in the soil is extracted from the ground to extract contaminated steam. I have. According to the method described in Japanese Patent Application Laid-Open No. 11-169837, a minute disturbance is caused between the soil fine particles by freezing, and thereafter, a gaseous pollutant existing in the unsaturated ground is suctioned. The pollutants are efficiently removed and the soil is purified.
[0004]
[Patent Document 1]
JP-A-11-169837 (Claim 1, paragraph number 0010)
[0005]
[Problems to be solved by the invention]
However, conventional methods of setting up tents around contaminated sites and removing contaminated soil by sealing them in drums, etc., do not provide sufficient measures to prevent harmful substances from evaporating during excavation and transportation and to prevent odors from waste. I can not say. In particular, when the harmful substance is a mercury compound or dioxin, it cannot be said that sufficient measures have been taken, and there remains a problem in terms of safety for workers and nearby residents. Further, the method for purifying contaminated ground described in Japanese Patent Application Laid-Open No. 11-169837 is a purification method for repairing contaminated ground, not a method for removing contaminated ground. In particular, since mercury compounds and dioxins need to be completely removed from the soil, it is necessary to excavate the soil containing the compounds and perform another treatment such as heating. Further, the conventional ground freezing method is intended to stabilize the ground by hardening the ground by freezing, and does not freeze the contaminated soil and take it out into the ground with the frozen soil.
[0006]
Therefore, an object of the present invention is to create a block-shaped frozen soil using freezing technology, to contain the odor of volatile substances and waste odors with ice, to reduce environmental risks more than before, and to reduce contaminated soil. It is an object of the present invention to provide a method for freezing and removing contaminated soil that enhances the removal and transport efficiency.
[0007]
[Means for Solving the Problems]
That is, the present invention is to solve the above-mentioned problem, and the present invention (1) provides a cooling pipe in a contaminated soil in which a contaminant is present such that the cooling pipes are arranged at equal distances between central portions. A cooling step of supplying a coolant to the cooling pipe to form a discontinuous frozen soil composed of a skin portion of the unfrozen soil and a remaining frozen soil around the cooling pipe; and a frozen soil for extracting the frozen soil portion of the discontinuous frozen soil to the surface of the ground. It is intended to provide a method for freezing contaminated soil having a removing step. According to the present invention, the contaminated soil can be formed into an aggregate in which a large number of block-shaped frozen soils are arranged by using a freezing technique and controlling the freezing condition. Since it can be pulled out by a towing machine such as a winch, loaded on a dump as it is, and carried out, the carrying-out efficiency is extremely excellent, and the volatilization of harmful substances and the odor of waste can be suppressed.
[0008]
In the present invention (2), a temperature leveling step in which the supply of the refrigerant is stopped and left for a predetermined time is performed between the cooling step and the frozen soil removing step, or the boundary between adjacent discontinuous frozen soils is heated. It is another object of the present invention to provide a method for freezing and removing the contaminated soil in which a pipe is installed and a heating step of heating the boundary portion is performed. According to the present invention, in addition to having the same effect as the above-described invention, in the cooling step, when the soil temperature at the intermediate point (boundary surface) of the cooling pipes adjacent to each other has substantially reached the target temperature, for example, 0 to 5 ° C. Then, the supply of the refrigerant is stopped, and then the temperature is leveled so that the temperature at the intermediate point becomes + 0 ° C., so that the area of the skin portion of the unfrozen soil can be minimized, and most of the The frozen soil can be easily carried out as a large cylindrical block. Further, if a heating step of forcibly heating the boundary portion between adjacent discontinuous frozen soils is performed instead of the temperature leveling step, the temperature of the boundary portion can be set to the target temperature in a short time, and the construction period can be shortened.
[0009]
In the present invention (3), in the cooling step, the coolant is supplied to a cooling pipe provided with at least one partial heat insulating part or at least one partial heating part in the middle in the depth direction, and divided into at least two blocks in the depth direction. It is an object of the present invention to provide a method for freezing and removing contaminated soil, which is a step of forming discontinuous frozen soil comprising a frozen skin portion and a remaining frozen soil around a cooling pipe. According to the present invention, in addition to having the same effects as the above-mentioned invention, it is necessary when the contaminated soil is deep and the depth exceeds one excavation. Even in the case where discontinuous frozen soil has to be used, the above-described improved cooling pipe can be used to divide it into a size suitable for unloading.
[0010]
Further, the present invention (4) is a frozen body in which a large number of columnar discontinuous frozen soils composed of a skin portion of unfrozen soil and a remaining frozen soil portion are arranged, and the centers of the discontinuous frozen soils adjacent to each other in a plan view. The present invention provides an underground frozen body that is arranged so that the distance between the clubs is equal. According to the underground frozen body of the present invention, the area ratio of discontinuous frozen soil in the entire design area (in plan view) exceeds 90%, and the area ratio of frozen ground in the entire design area (in plan view) exceeds 80%. Exceed. Further, since the skin portion of the unfrozen soil has low strength, the block-shaped frozen soil can be pulled up to the ground without any trouble. In addition, the block-shaped frozen soil in which harmful substances are sealed can be carried out as it is on a dump or the like. Also, if a wedge or the like is driven into the boundary surface of the discontinuous frozen soil, the adjacent block-shaped frozen soil can be surely sectioned, and the lifting to the surface of the ground becomes easier.
[0011]
The present invention (5) provides the underground frozen body in which the discontinuous frozen soil is divided into at least two blocks in the depth direction. According to the present invention, in addition to exhibiting the same effects as the above-described invention, even in the case of contaminated soil deep in the depth direction, it is vertically divided into dimensions suitable for carrying out, and the divided block-shaped frozen soil can be easily formed. Can be raised.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for freezing and removing contaminated soil according to the present invention includes a cooling pipe arranging step of arranging a cooling pipe on the contaminated soil in which a contaminant is present such that the distance between the centers is equal, and supplying a coolant to the cooling pipe. A cooling step of forming discontinuous frozen soil composed of a skin portion of unfrozen soil and a remaining frozen soil around the cooling pipe; and a frozen soil removing step of extracting a frozen soil portion of the discontinuous frozen soil to the surface of the ground. Hereinafter, each step will be described with reference to FIGS. FIG. 1 is a schematic plan view after the cooling step, and FIG. 2 is a schematic sectional view of the underground frozen body after the cooling step.
[0013]
(Cooling pipe installation process)
In the present invention, the contaminated soil is not particularly limited as long as a contaminant is present in the soil below the ground surface, and the ground may be a sandy soil, a clay layer, a natural ground such as an alternate layer, and a waste treatment. Ground, sludge treatment plant ground, and reclaimed artificial ground. Among them, the ground in which the contaminants exist near the ground surface or at a depth of about 10 m from the ground surface is particularly advantageous in that it is easily removed by freezing. The contaminants are not particularly limited, and include, for example, mercury compounds, dioxins, benzene, trichloroethylene, tetrachloroethylene, and the like. In addition to these, there are also pollutants that emit odors.
[0014]
Next, cooling pipes are arranged so that three contiguous soils, for example, 6a, 6b, and 6c in FIG. 1, come to the vertices of an equilateral triangle. The distance between the cooling pipes (between 6a and 6b, between 6b and 6c, and between 6a and 6c in FIG. 1) is not particularly limited, but is, for example, 1.5 to 3.0 m, and preferably 1.7 to 3.0 m. 2.5 m. By forming an equilateral triangle arrangement, the area ratio of the partially frozen soil in the entire target area can be increased, and the number of days required for freezing can be reduced. If the distance between the cooling pipes is less than 1.5 m, the number of cooling pipes increases, which is uneconomical. On the other hand, if it exceeds 3.0 m, it is necessary to take many days required for freezing, and the energy loss becomes large. In the conventional ground freezing method, the ground is hardened by freezing to stabilize the ground. The contaminated soil is frozen into a large number of cylindrical blocks, and the block-shaped frozen soil is taken out one by one to the surface of the ground. It is not an idea.
[0015]
The cooling pipes are for forming frozen soil of a columnar block around the cooling pipes, and are provided in large numbers in the design area of the contaminated soil at the above-mentioned distance intervals. The same cooling pipe as that used in the known underground freezing method can be used. As a known underground freezing method, a refrigerant called brine is cooled to −20 ° C. to −30 ° C. using a refrigerator, and is sent to a cooling pipe buried in the ground by a circulation pump to cool the ground. Construction method. The underground depth of the cooling pipe is appropriately determined depending on the depth of the contaminated soil, the frozen soil temperature, and the like. In order to prevent the surrounding ground from collapsing when the frozen soil is drawn to the ground surface in the frozen soil removing step, it is preferable that a frozen soil retaining wall having a continuous and uniform temperature is formed around the frozen soil. preferable.
[0016]
(Cooling process)
As shown in FIG. 1, the cooling process is performed by supplying a coolant to the cooling pipe 1 and forming a discontinuous frozen soil composed of a skin portion 12 of the unfrozen soil in a small area and a frozen soil 11 inside the skin portion and most of the remaining frozen soil 11. 2 is a step of forming around the cooling pipe 1. In the cooling step, the temperature of the refrigerant supplied to the cooling pipe 1 is -15C to -30C, preferably -20C to -30C. When the temperature of the refrigerant is about -5 to -10C, the supply period of the refrigerant becomes too long, and the energy efficiency is poor. Although the supply period of the refrigerant is not particularly limited, it is usually 20 to 120 days because the underground temperature is usually about 20 ° C. and most of the underground is frozen.
[0017]
In the cooling step, the coolant is continuously supplied to the cooling pipe 1 for the number of days described above so that the temperature of the boundary portion 9 of the discontinuous frozen soil 2 becomes the target temperature. The target temperature is, for example, 0 to 2 ° C. If the target temperature is below the freezing point, heating is necessary to create unfrozen soil in the skin, which is a waste of energy. On the other hand, if the temperature exceeds 2 ° C., the temperature leveling period after the cooling step becomes longer, or the unfrozen soil portion becomes too thick, and the efficiency of removing the frozen soil portion is deteriorated. In the cooling step, even if the temperature of the boundary portion 9 of the discontinuous frozen soil 2 is in the range of 0 to 2 ° C., the temperature of the frozen soil portion 11 around the cooling pipe 1 is, for example, −20 to −30 ° C. of the temperature of the refrigerant. . The cooling process ends when the supply of the refrigerant to the cooling pipe 1 is stopped.
[0018]
(Temperature leveling process)
The temperature leveling step is an optional step, in which the supply of the refrigerant to the cooling pipe is stopped and then left for a predetermined time to level the temperature of the discontinuous frozen soil. At the time when the supply of the refrigerant is stopped in the cooling process, if the soil temperature of the intermediate point between the cooling pipes 1 and 1 adjacent to each other, that is, the soil temperature of the boundary portion 9 is close to the target temperature of 5 ° C., the boundary portion is left for a while. The temperature leveling is performed so that the temperature of No. 9 is about + 0 ° C. and the temperature of the frozen soil part 11 is about −0 to −3 ° C. The predetermined time for leaving the work is, for example, 5 to 15 days. By leveling the temperature, it is possible to minimize the area of the skin portion 12 of the unfrozen soil, and to easily carry out the remaining frozen soil 11 in a large block shape. In addition, it is preferable to install an instrument for distinguishing between unfrozen and frozen on the skin, since freezing of the skin can be reliably prevented. Such instruments include thermometers and electrical resistors. It is particularly preferable to install the thermometer and the electric resistor in combination.
[0019]
(Heating process)
The heating step is an optional step, in which a heating pipe is provided at a boundary portion between adjacent discontinuous frozen soils to heat the boundary portion. This can be performed when the soil temperature at the boundary portion 9 which is an intermediate point between the cooling pipes 1 and 1 adjacent to each other in the cooling step is excessively cooled, or as an alternative to the temperature leveling step. That is, in this heating step, the boundary portion 9 of the adjacent discontinuous frozen soil is forcibly heated, so that the temperature of the boundary portion can be reliably raised to a temperature above the freezing point in a short time, and the strength of the ground in such a portion decreases. As a result, the construction period can be shortened. When the heating pipe is to be used in advance, the heating pipe may be provided at an intermediate position between the adjacent cooling pipes 1 and 1 during the cooling pipe providing step, or may be provided before the heating step is started. Good.
[0020]
In the present invention, the cooling pipe 1 is removed from the contaminated ground 4 after the cooling step. Also, when performing the temperature leveling step or the heating step, even after the cooling step, or may be after the temperature leveling step or the heating step, even in this case, immediately after the cooling step, already It is preferable that the contaminated soil that has been frozen can be carried out immediately after the temperature leveling step or the heating step without having to leave the used member. The cooling pipe 1 can be easily pulled out of the frozen soil 11 by flowing hot water through the cooling pipe 1 for several tens of minutes. When the cooling pipe 1 is used as a fixing part to which a winch or the like is attached, the cooling pipe 1 may not be pulled out.
[0021]
After the cooling process, or in the case where the temperature leveling process or the heating process is performed, the frozen ground formed in the ground after the process includes, as shown in FIG. An aggregate in which a large number of columnar discontinuous frozen soils 2 composed of a skin portion 12 and the remaining frozen soil 11 occupying most of the area are arranged, and three central portions of the discontinuous frozen soils 2 adjacent to each other in plan view. Are arranged at equal distances. The cooling pipe 1 has already been drawn from the underground frozen body 10 in FIG. 2, and the trace of the cooling pipe 1 forms a hollow portion 13. Although the size of one discontinuous frozen soil 2 is not particularly limited, it is, for example, 2 m in diameter and 2 m in depth. The area ratio of the frozen soil 11 is, for example, 80 to 90%, preferably 85 to 90% of the diameter of the discontinuous frozen soil.
[0022]
(Freeze removal process)
The freeze removal step is a step of drawing the frozen ground 11 of the discontinuous frozen ground 2 to the surface of the ground. In the discontinuous frozen soil 2, since the skin portion 12 is non-frozen soil, the frozen soil portion can be drawn out to the ground surface as one block. That is, if the connection fitting 52 is driven into the head of the frozen ground 11 and pulled through the wire 54 by a pulling machine such as a winch, the connection can be directly loaded on the dump and carried out, so that the carrying out efficiency is extremely excellent. Further, if the wedge 53 or the like is driven into the boundary portion 9 of the discontinuous frozen soil 2, the division becomes more reliable, and the lifting to the ground surface becomes easier (see FIG. 5).
[0023]
According to the underground frozen body 10 of the present invention, the area ratio of the discontinuous frozen soil in the entire design area (in plan view) exceeds 90%, and the area ratio of the frozen ground in the entire design area (in plan view) is 80%. Exceeds. Further, since the skin portion of the unfrozen soil has low strength, the block-shaped frozen soil can be pulled up to the ground without any trouble. In addition, the block-shaped frozen soil in which harmful substances are sealed can be carried out as it is on a dump or the like. At this time, the harmful substances are sealed with ice, so that the volatilization of the harmful substances and the odor of the waste can be suppressed.
[0024]
Further, in the present invention, in the cooling pipe arranging step, it is preferable that a thermometer for temperature measurement is arranged in each part of the contaminated soil simultaneously with the arrangement of the cooling pipe. Thereby, discontinuous frozen soil can be efficiently and reliably obtained. Also, after arranging cooling pipes on the contaminated soil at a predetermined pitch and before entering the cooling process, covering the ground surface with a sheet prevents heat from flowing into the cooling ground from the atmosphere and prevents rainfall. This is preferable in that the inflow of water can be prevented. Further, the sheet is removed after the cooling step, or when the temperature leveling step or the heating step is performed, thereafter and before the excavation step.
[0025]
In the present invention, a modified cooling pipe can be used in the cooling step. FIG. 3 is a schematic view of the modified cooling pipe 1. The modified cooling pipe is a conventional cooling pipe provided with a partial heat insulating portion in the middle in the depth direction. That is, the modified cooling pipe 1a has a belt-like heat insulating material 34 attached to the inner peripheral surface of the outer cylinder in the depth direction of the cooling pipe main body 35, and cools from the outer cylindrical surface 33 of the heat insulating material 34. And cooling from the other outer cylinder surface 32 is performed. The same effect can be obtained by installing a band-shaped heater instead of the band-shaped heat insulating material 34. Reference numeral 31 denotes a refrigerator, and a downward arrow indicates supply of the refrigerant, and an upward arrow indicates return of the refrigerant.
[0026]
When a cooling process is performed using such a cooling pipe 1a, as shown in FIG. 4, a discontinuity consisting of an unfrozen soil surface portion 12 divided into two blocks in the vertical direction and a remaining frozen soil 11 is formed. The frozen soil 2a, 2b can be formed around the cooling pipe 1.
The form of the divided portion 8 includes a form in which the upper and lower blocks are completely divided, and a form in which a small amount of frozen soil is formed around the cooling pipe 1 and the upper and lower blocks are continuous. Even if the upper and lower two blocks are continuous with a slight amount of frozen soil, the continuous portion is broken if a wedge or a traction machine is operated, so that there is no problem in raising the ground to the ground. Note that the number of heat insulating materials is not limited to one, and a plurality of heat insulating materials can be provided at an appropriate pitch according to the depth.
[0027]
In the case of the conventional cooling pipe 1, when a harmful substance exists deeply in the depth direction, a long block-shaped discontinuous frozen soil has to be formed. In this case, it is difficult to extract one frozen soil to the surface of the ground, and it is possible that the lifted frozen soil is too large to be used for dumping. However, as shown in FIG. 5, if the underground frozen body 10a is formed with a large number of discontinuous frozen soils 2a, 2b divided into two blocks in the vertical direction, a suitable size for carrying out the block-shaped frozen soil is provided. , So that the unloading efficiency is improved. In FIG. 5, reference numeral 51 denotes a crane.
[0028]
【The invention's effect】
According to the present invention, the contaminated soil can be formed into an aggregate in which a large number of block-shaped frozen soils are arranged by using a freezing technique and controlling the freezing condition. Since it can be pulled out by a towing machine such as a winch, loaded on a dump as it is, and carried out, the carrying-out efficiency is extremely excellent, and the volatilization of harmful substances and the odor of waste can be suppressed.
According to the present invention, in addition to having the same effects as the above invention, in the cooling step, the soil temperature at the midpoint (boundary surface) of the cooling pipes adjacent to each other has almost reached the target temperature, for example, 0 to 2 ° C. At this point, the supply of the refrigerant is stopped, and then the temperature is leveled so that the temperature at the intermediate point becomes a temperature of + 0 ° C., so that the area of the skin portion of the frozen ground can be minimized, and Part of the frozen soil can be easily carried out as a large columnar block. Further, if a heating step of forcibly heating the boundary portion between adjacent discontinuous frozen soils is performed instead of the temperature leveling step, the temperature of the boundary portion can be set to the target temperature in a short time, and the construction period can be shortened.
Further, according to the present invention, in addition to having the same effect as the above invention, even in the case where the contaminated soil is deep and the conventional cooling pipe is forced to be a block-shaped discontinuous frozen soil long in the depth direction. Since the above-described improved cooling pipe is used, the cooling pipe can be vertically divided into dimensions suitable for carrying out.
[0029]
Further, according to the underground frozen body of the present invention, the area ratio of the discontinuous frozen soil in the entire design area (in plan view) exceeds 90%, and the area ratio of the frozen ground in the entire design area (in plan view) is 80%. %. Further, since the skin portion of the unfrozen soil has low strength, the block-shaped frozen soil can be pulled up to the ground without any trouble. In addition, the block-shaped frozen soil in which harmful substances are sealed can be carried out as it is on a dump or the like. Also, if a wedge or the like is driven into the boundary surface of the discontinuous frozen soil, the adjacent block-shaped frozen soil can be reliably separated, and the lifting to the surface of the ground becomes easier.
Further, according to the present invention, in addition to the same effects as those of the above-described invention, it is possible to easily pull up the block-shaped frozen soil which is vertically divided into a size suitable for carrying out.
[Brief description of the drawings]
FIG. 1 is a schematic view in plan view after a cooling step.
FIG. 2 is a schematic sectional view of an underground frozen body after removing a cooling pipe.
FIG. 3 is a schematic view of a modified cooling pipe.
FIG. 4 is a schematic cross-sectional view of an underground frozen body in another embodiment after removing a cooling pipe.
FIG. 5 is a diagram illustrating a step of freezing an underground frozen object in another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cooling pipe 2, 2a, 2b Discontinuous frozen soil 3 Unfrozen part other than skin part 4 Contaminated ground 6a, 6b, 6c Central part of discontinuous frozen soil 8 Divided part 9 Intermediate point (boundary part) of adjacent cooling pipes
10, 10a Underground frozen part 11 Frozen soil 12 Skin part (unfrozen soil)

Claims (5)

A cooling pipe arranging step of arranging a cooling pipe on the contaminated soil in which the contaminant is present so that the distance between the center portions is equal, and supplying a coolant to the cooling pipe to form a skin portion of the unfrozen soil and the remaining frozen soil. A method for freezing and removing contaminated soil, comprising: a cooling step of forming discontinuous frozen soil around a cooling pipe, and a frozen soil removing step of extracting a frozen soil portion of the discontinuous frozen soil to the surface of the ground. Between the cooling step and the frozen soil removing step, a temperature leveling step in which the supply of the refrigerant is stopped and left for a predetermined time is performed, or a heating pipe is installed at a boundary part of the adjacent discontinuous frozen soil, and the boundary part is provided. The method for freezing and removing contaminated soil according to claim 1, wherein a heating step of heating the contaminated soil is performed. The cooling step supplies a refrigerant to a cooling pipe provided with at least one partial heat insulating portion or partial heating portion in the middle of the depth direction, and a skin portion and a remaining portion of the frozen ground divided into at least two blocks in the depth direction. 3. The method for freezing and removing contaminated soil according to claim 1 or 2, wherein a step of forming discontinuous frozen soil comprising the frozen soil around the cooling pipe is performed. It is a frozen body in which a large number of columnar discontinuous frozen soils composed of a skin portion of unfrozen soil and a remaining frozen soil portion are arranged, and the center portions of the discontinuous frozen soils adjacent to each other in plan view are equidistant. An underground frozen body that is provided. The underground frozen body according to claim 4, wherein the discontinuous frozen soil is divided into at least two blocks in the depth direction.

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