JP6273666B2 - Contaminated soil purification method and system in shield method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a contaminated soil purification method in a shield method, and specifically, a technique that efficiently and reliably purifies excavated soil containing heavy metals and can reduce disposal costs of excavated soil in the shield method. About.

  The shield method that can underpass roads and railroad tracks with a small cover thickness and can be used for tunnel excavation in a wide range of ground conditions is expanding its application range in the present situation where difficult construction conditions are increasing. On the other hand, there are areas where heavy metals are included in the ground to be excavated by such a shield method, and in that case, excavated soil and insolubilized material may be mixed as necessary to prevent heavy metals from eluting to the surroundings. Conventional contaminated soil treatment techniques using insolubilizing materials include the following.

  For example, excavation residue generated when pipes are constructed using a sealed shield tunnel method in a contaminated soil area of heavy metals (arsenic, cyanide, mercury, hexavalent chromium, lead, cadmium, fluorine, boron) A method of insolubilizing heavy metals contained in the surface of the face of a hermetic shield machine (see Patent Document 1) has been proposed.

  Further, a step of adding a soil cleaner with a shield face to the ground, a step of stirring and mixing the excavation soil containing the cleaner taken into the chamber of the shield excavator with stirring means, There has also been proposed a method (see Patent Document 2) including a step of conveying agitated excavated soil out of the chamber.

  In addition, the solid content is separated from the discharged mud water discharged by the muddy water shield machine, a part of the muddy water is discharged as surplus mud water from the storage tank storing the remaining mud water, and an insolubilizing agent is mixed with this. Technology (see Patent Document 3) has also been proposed.

JP 2006-316599 A JP 2012-120987 A Japanese Patent No. 5001100

  By performing the insolubilization described above, the diffusion of heavy metals to the surrounding environment by elution is surely suppressed. However, although heavy metals are insolubilized, they are still present in the excavated soil, so depending on the local government that accepts the excavated soil as construction generated soil, the excavated soil treated in this way may be It may be considered as industrial waste instead. In this case, the disposal cost of excavated soil becomes high, leading to an increase in the cost of the entire tunnel construction. In addition, when excavating soil generated in the underground shield excavation system is to be transported to an above-ground processing facility for insolubilization, it is necessary to secure equipment and its operating area for carrying out, so that construction costs and construction efficiency It is easy to invite deterioration. Furthermore, there is a concern that the excavated soil may be scattered and diffused during the carry-out, and efficient and reliable treatment cannot be performed.

  Therefore, an object of the present invention is to provide a technique capable of efficiently and reliably purifying excavated soil containing heavy metals and reducing disposal costs of excavated soil in the shield method.

How contaminated soil remediation in shield method of the present invention for solving the above-mentioned problems, the excavated soil generated by mud water type shield tunneling, was added iron powder to adsorb heavy metals, the excavated soil the iron powder with adsorbed heavy metals In the muddy water treatment system that separates muddy water and excavated soil, after separating construction generated soil from muddy water in a primary treatment machine, the iron powder is added to the muddy water. And the said iron powder which adsorb | sucked the heavy metal is isolate | separated from the said muddy water with the separator using a specific gravity difference.

  According to this, it becomes possible to make the excavated soil harmless by separating the adsorbent adsorbing the heavy metal from the excavated soil. Therefore, even in the situation where there are strict standards for accepting residual soil, excavated soil can be disposed of as general residual soil, and the disposal cost is low. In addition, since a series of operations are performed in the shield excavation system, the contaminated soil is not scattered or diffused to the external environment.

Further, the contaminated soil purification system in the shield method of the present invention includes an addition device for adding iron powder that adsorbs heavy metals to the excavated soil generated by the muddy water type shield method, and the iron powder that adsorbs heavy metals from the excavated soil. A contaminated soil purification system in a shield method, comprising a separating device for separating, wherein the adding device is a device for adding the iron powder to the muddy water in a muddy water treatment system for separating muddy water and excavated soil, The separation device is a device that separates the iron powder having adsorbed heavy metal from the muddy water using a specific gravity difference .

  According to the present invention, in the shield method, excavated soil containing heavy metals can be purified efficiently and reliably, and the disposal cost of excavated soil can be reduced.

It is a figure which shows Example 1 of the contaminated soil purification system in the shield construction method of 1st Embodiment. It is a figure which shows the example of a procedure of the contaminated soil purification method in the shield construction method of 1st this embodiment. It is a figure which shows Example 2 of the contaminated soil purification system in the shield construction method of 1st Embodiment. It is a figure which shows Example 3 of the contaminated soil purification system in the shield construction method of 1st Embodiment. It is a figure which shows the example of the contaminated soil purification system in the shield construction method of 2nd Embodiment. It is a figure which shows the example of a procedure of the contaminated soil purification method in the shield construction method of 2nd Embodiment. It is a figure which shows the other example of the contaminated soil purification system in the shield construction method of 2nd Embodiment.

--- First Embodiment ---
Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram illustrating Example 1 of a contaminated soil purification system in the shield method according to the first embodiment, and FIG. 2 is a diagram illustrating a procedure example of the contaminated soil purification method in the shield method according to the first embodiment. Here, as one of the shield construction methods, a contaminated soil purification method and system when the muddy water shield construction method is adopted will be described. The muddy water type shield method is a shield method in which the inside of the chamber of the shield machine 10 is filled with muddy water, and the pressure of this muddy water opposes the face soil pressure and groundwater pressure to stabilize the face surface. By controlling the muddy water pressure in the chamber, it is possible to flexibly counter the face soil pressure and groundwater pressure and to excavate in a stable state corresponding to a wide range of geology.

  In the contaminated soil remediation system 100 illustrated in FIG. 1, the shield machine 10 rotates the cutter head 11 to excavate the face, and mixes the sand and excavated soil cut by the cutter head 11 with mud water. This is pumped out of the mine by the mud pump 12 (s100). In the case of a conventional shield excavation system that does not purify contaminated soil, the muddy water pumped backward by the mud pump 12 is sent to the solid-liquid separator 20 as it is through the mud discharge system 14 such as a mud pipe. . This solid-liquid separator 20 is a muddy water treatment system that separates muddy water and excavated soil. The muddy water is treated with a primary treatment device 21 such as a vibrating screen, a muddy water is temporarily stored, and an adjustment tank 22 for adjusting components, and centrifugal separation. It is separated into construction generated soil derived from excavated soil (extracted by the primary processor 21), construction sludge (extracted by the secondary processor 23), and mud water by the secondary processor 23 such as a vessel. Further, the mud separated by the solid-liquid separator 20 is supplied again to the face through a mud supply system 17 such as a mud pipe or a mud pump 16.

  On the other hand, the contaminated soil purification system 100 according to the present embodiment for purifying the contaminated soil includes an adsorbent addition device 18 in addition to the mud pump 12 in the above-described mud discharge system 14. The adsorbent addition device 18 adds an adsorbent that adsorbs heavy metals to the mud supplied from the mud pump 12 (s101). The adsorbent addition device 18 includes a tank that stores a predetermined amount of adsorbent, and a mixing device that continuously acquires a predetermined amount of adsorbent from the tank and adds it to the mud drained.

  In addition, iron powder is mention | raise | lifted as an adsorbent which the adsorbent addition apparatus 18 adds to muddy water. It is known that iron powder has the property of adsorbing and immobilizing heavy metals such as arsenic, selenium, hexavalent chromium, cadmium, lead, and cyan efficiently. Therefore, by adding and mixing this iron powder to the muddy water containing the excavated soil, the heavy metal fine particles adhering to the excavated soil particles in the muddy water are adsorbed on the iron powder surface and fixed to the iron powder. . In the following description, the adsorbent is assumed to be iron powder.

  The muddy water to which the iron powder has been added by the adsorbent addition device 18 is efficiently mixed with the iron powder in accordance with changes in the flow path, flow velocity, etc. in the mud pipe while passing through the mud pipe. That is, even if a stirring means or the like is not separately provided, the heavy metal particles attached to the excavated soil in the muddy water are sufficiently in contact with the iron powder and adsorbed on the iron powder surface. The muddy water to which the iron powder has been added in this way is supplied to the magnetic separator 19 through the mud pipe (s102). The magnetic separator 19 supplied with the muddy water separates the iron powder from the muddy water (s103).

  The magnetic separator 19 includes a rotating drum incorporating a permanent magnet that exerts a magnetic force with a predetermined strength on the muddy water, and a scraper that scrapes and collects iron powder adhering to the rotating drum surface from the rotating drum surface by the magnetic force of the permanent magnet. At least. In the case of a structure using an electromagnet instead of a permanent magnet, the magnetic separator 19 has a rotating drum and an electromagnet control device incorporating an electromagnet that generates a magnetic force of a predetermined strength in muddy water at a constant cycle, and the surface of the rotating drum by the magnetic force of the electromagnet. And a scraper that scrapes and collects the adhering iron powder in accordance with the stop of magnetic force generation by the electromagnet. The iron powder collected by the magnetic separator 16 becomes contaminated iron powder on which heavy metal particles are adsorbed.

  In addition, as a separation apparatus which isolate | separates adsorbent from muddy water, you may use the separation apparatus using the specific gravity difference of the earth and sand in muddy water, and the adsorbent which adsorb | sucked the heavy metal other than the above-mentioned magnetic separator 19. FIG. Moreover, it is also possible to add a drug or the like that releases adsorption of iron powder and heavy metal to the contaminated iron powder, separate the heavy metal from the contaminated iron powder, and use the separated heavy metal as a resource.

  Thereafter, the contaminated iron powder is separated and detoxified, and the muddy water is supplied to the solid-liquid separator 20 (s104). In the solid-liquid separator 20, the soil having a relatively large particle size including muddy water is taken out by the primary processing machine 21 and is not generated as construction soil (s <b> 105), and the muddy water having only the small particle size is adjusted in the adjustment tank. The water is temporarily stored at 22, and the components are adjusted to the properties (specific gravity, etc.) necessary as mud water for supplying the face by appropriately adding water and mud (s106). The muddy water adjusted to the necessary properties in the adjustment tank 22 is supplied again to the face through the muddy water supply system 17 (s107). On the other hand, the surplus muddy water in the adjustment tank 22 is supplied to the secondary treatment machine 23 and separated into slime-like construction sludge containing only a very small particle size of soil and treated water (s108). The treated water separated in the adjustment tank 22 is supplied to the mud tank 24 and used for making mud water to be supplied to the adjustment tank 22 (s109). The mud tank 24 is a device that mixes the treated water with bentonite and the like to generate mud water and supplies the generated mud water to the adjustment tank 22 as necessary. The muddy water in the adjustment tank 22 is supplied to the face by the mud pump 16 via the mud pipe of the muddy water supply system 17 (s110), and the above processing (steps s100 to s109) is repeated.

  In the example described above, the adsorbent addition device 18 is provided in the muddy water carrying-out system 14, but the adsorbent addition device 18 may be provided in the muddy water supply system 17 as in the contaminated soil purification system 100 shown in FIG. Good. In this case, the mud pump 16 sucks up the muddy water from the adjustment tank 22 and supplies it to the adsorbent adding device 18A. The adsorbent addition device 18A has the same configuration as the adsorbent addition device 18 described above, and adds the adsorbent to the muddy water supplied from the mud pump 16. The muddy water to which the adsorbent is added is supplied to the face via the mud pipe of the muddy water supply system 17. The muddy water supplied to the face is mixed with the earth and sand of the face, that is, excavated soil, together with the cutting operation accompanied by the rotation of the cutter head 11, and is pumped backward by the mud pump 12. The subsequent processing is the same as the processing after the processing (step s103) in the magnetic separator 19 described above. When adsorbent addition is performed on the muddy water supplied to the face, the distance between the adsorbent addition device 18A and the magnetic separator 19 is longer than when the adsorbent addition device 18 described above is provided in the mud discharge system 14. That is, the contact time between the adsorbent and the muddy water becomes longer, and the adsorption efficiency of heavy metals on the adsorbent becomes better.

  In addition, as illustrated in FIG. 4, an adsorbent may be added and recovered by the solid-liquid separator 20 that is a muddy water treatment system. In this case, the adsorbent addition device 18 </ b> B is disposed behind the adjustment tank 22, and the magnetic separator 19 </ b> B is disposed between the adsorbent addition device 18 and the secondary processing device 23. Therefore, the surplus mud in the adjustment tank 22 is supplied to the adsorbent adding device 18B, and the adsorbent is added to the mud. The muddy water to which the adsorbent has been added is sent to the magnetic separator 19B, where the iron powder is separated from the muddy water by the magnetic separator 19B. The contaminated iron powder is separated and made harmless by the magnetic separator 19B, and supplied to the secondary processor 23. The processing after the secondary processor 23 is the same as that after step s108 described above. If it is set as such a form, admixture of adsorbents does not occur in the mud circulation system for working faces, such as the mud discharge system 14 and the mud supply system 17, and wear of the piping due to the adsorbent (iron powder) can be avoided.

  Further, the adsorbent addition device may be provided in all or any two of the muddy water carry-out system 14, the muddy water supply system 17, and the solid-liquid separation device 20 (muddy water treatment system). In this case, if a longer contact time between the adsorbent and the muddy water is required, such as when the excavated soil has a coarse particle size or is hard, according to the change in the ground property of the face, the adsorption provided in the muddy water supply system 17 When the material addition device 18A is operated and there is no problem even if the contact time between the adsorbent and the mud is not long, such as when the excavated soil has a fine particle size or high viscosity, the adsorbent addition device provided in the mud discharge system 14 18 is operated and the adsorbent is added when it is determined that the treatment in the solid-liquid separation device 20 rather than the mud discharge system 14 or the mud supply system 17 is suitable depending on the properties and amount of the mud to be treated or the heavy metal content. It can be assumed that the operation switching control between the adsorbent addition devices, such as operating the device 18B (and the magnetic separator 19B), is performed. Magnetic separators may also be provided at a plurality of locations in the contaminated soil purification system 100. The location where each magnetic separator is installed is located in the piping path included in the contaminated soil purification system 100 downstream of the adsorbent addition device by a predetermined distance, and after adsorbent addition by the adsorbent addition device, mud water and This is where the adsorbent can secure a predetermined contact time. In addition, a plurality of magnetic separators may be provided in series at each location or at any location for the purpose of increasing the recovery rate of the adsorbent.

--- Second Embodiment ---
Then, the contaminated soil purification method and system at the time of employ | adopting the earth pressure type shield method as one of the shield methods are demonstrated. FIG. 5 is a diagram illustrating an example of a contaminated soil purification system in the shield method according to the second embodiment, and FIG. 6 is a diagram illustrating a procedure example of the contaminated soil purification method in the shield method according to the second embodiment. In the earth pressure shield method, an appropriate mud-making material is added to the earth and sand excavated by the cutter head 31 to form a mud having impermeability and plastic fluidity, and then filled in the chamber and screw conveyor. This is a construction method that stabilizes the face by generating mud pressure.

  In the contaminated soil purification system 200 illustrated in FIG. 5, the shield machine 30 rotates the cutter head 31 to excavate the face, and water or an additive is added to the sand or excavated soil cut by the cutter head 31. (Mud soil material) is mixed to generate a mud having impermeability and plastic fluidity and filled in the chamber and the screw conveyor (s200).

  Further, the shield machine 30 discharges the mud described above to the fluidizing device 44 in the mud unloading system 33 by the screw conveyor 32. The fluidizing device 44 adds water to the discharged mud, that is, excavated soil, and creates a slurry-like fluid that can be pumped by the mud pump 35 (s201). On the other hand, the adsorbent adding device 34 adds iron powder to the fluid discharged from the fluidizing device 44 (s202). The adsorbent addition device 34 includes a tank that stores a predetermined amount of iron powder, and a mixing device that continuously acquires a certain amount of iron powder from the tank and adds it to the fluid.

  The fluid containing the iron powder generated by the adsorbent addition device 34 is efficiently mixed with the iron powder in accordance with changes in the flow path and flow velocity in the mud pipe in the process of passing through the mud pipe. . That is, even if a stirring means or the like is not separately provided, the heavy metal particles attached to the excavated soil in the muddy water are sufficiently in contact with the iron powder and adsorbed on the iron powder surface. Thus, the muddy water containing the iron powder is supplied to the magnetic separator 37 through the mud pipe (s203). The magnetic separator 37 that has received the supply of muddy water separates and collects iron powder from the muddy water (s204). The iron powder recovered here becomes contaminated iron powder on which heavy metal particles are adsorbed.

  Thereafter, the contaminated iron powder is separated and detoxified, and the fluid is supplied to the water content ratio adjuster 38 (s205). The water content ratio adjuster 38 executes a predetermined dehydration process using a vibration sieve, a filter press or the like, and lowers the water content ratio of the muddy water, which has a high water content ratio, to form construction generated soil (s206). The water content ratio adjuster 38 supplies the treated water obtained by the process of adjusting the water content ratio to the humidified material supply system 39 and the fluidizing device 44 (s207).

  The treated water supplied to the mud material supply system 39 is transported to the liquid producing tank 40 and used to create the mud material supplied to the face (s208). The liquid production tank 40 mixes this treated water with an appropriate chemical or the like to generate a mud material, and supplies it to the face via the pressure feed pump 41 and the pressure feed pipe 42 (s209). Thereafter, the above processing (steps s200 to s208) is repeated.

  In the above-described example, the adsorbent addition device 34 is provided in the mud unloading system 33. However, as shown in FIG. 7, the adsorbent addition device 34 may be provided in the mud supply material supply system 39. In this case, the adsorbent addition device 34 </ b> A is configured to add an adsorbent such as iron powder to the liquid production tank 40. The adsorbent addition device 34A has the same configuration as the adsorbent addition device 34 described above. The mud material to which the adsorbent is added is supplied to the face via the pressure feed pipe 42 of the mud material supply system 39. The mud material supplied to the face is well kneaded with the earth and sand of the face, that is, excavated soil, along with the cutting operation accompanied by the rotation of the cutter head 31, and is pumped backward by the mud pump 35. Therefore, the mixing of the excavated soil and the iron powder is efficiently performed by the above-described kneading by the rotation of the cutter head 31, and it is not necessary to separately provide a stirring means or the like. The subsequent processing is the same as the processing after the processing (step s204) in the magnetic separator 37 described above. When the adsorbent is added to the mud material supplied to the face, the distance between the adsorbent addition device 34A and the magnetic separator 37 is compared with the case where the above-described adsorbent addition device 34 is provided in the mud unloading system 33. In other words, the contact time between the adsorbent and the mud becomes longer, and the adsorption efficiency of heavy metals on the adsorbent becomes better. Moreover, it is good also as providing an adsorbent addition apparatus in both the mud unloading system | strain 33 and the mud material supply system | strain 39, that the magnetic separator 37 may be installed in several places, and the several magnetic separator 37 is provided. It is the same as that of the above-mentioned muddy water type shield construction method that it may be provided in series at each location or at any location. Further, it is conceivable that the adsorbent addition device 34 is incorporated in a system of treated water added to fluidize excavated soil. Further, an adsorbent may be added to the excavated soil outside the tunnel, that is, on the ground, or in some cases, in the tunnel completion section behind the contaminated soil purification system.

  As described above, according to the present embodiment, excavated soil containing heavy metals can be efficiently and reliably purified in the shield method, and the disposal cost of excavated soil can be reduced.

  As mentioned above, although embodiment of this invention was described concretely based on the embodiment, it is not limited to this and can be variously changed in the range which does not deviate from the summary.

DESCRIPTION OF SYMBOLS 10, 30 Shield machine 11, 31 Cutter head 12 Mud pump 14 Mud discharge system 16 Mud pump 17 Mud supply system 18, 18A, 18B Adsorbent addition device 19, 19B Magnetic separator 20 Solid-liquid separation device 21 Primary processor 22 Adjustment tank 23 Secondary processing machine 24 Mud tank 32 Screw conveyor 33 Mud carry-out system 34, 34A Adsorbent addition device 35 Mud pump 37 Magnetic separator 38 Moisture content adjustment machine 39 Additive material supply system 40 Fluid tank 41 Pressure feed pump 42 Pressure feed pipe 44 Fluidization apparatus 100, 200 Contaminated soil purification system

Claims (2)

A method for purifying contaminated soil in a shield method, wherein iron powder that adsorbs heavy metals is added to excavated soil generated by the muddy water shield method, and the iron powder that adsorbs heavy metals is separated from the excavated soil,
In a muddy water treatment system that separates muddy water and excavated soil, after separating construction generated soil from muddy water with a primary treatment machine, the iron powder was added to the muddy water, and heavy metals were adsorbed with a separation device using specific gravity difference A method for purifying contaminated soil in a shield method, wherein the iron powder is separated from the muddy water. Contaminated soil purification in the shield method, comprising an addition device for adding iron powder that adsorbs heavy metals to the excavated soil generated by the muddy water shield method, and a separation device for separating the iron powder adsorbed heavy metals from the excavated soil A system,
The addition device is a device for adding the iron powder to the muddy water in a muddy water treatment system for separating muddy water and excavated soil,
The said separation apparatus is an apparatus which isolate | separates the said iron powder which adsorb | sucked heavy metal from the said muddy water using a specific gravity difference, The contaminated soil purification system in a shield construction method characterized by the above-mentioned.

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