JP2012120987A - Method for purifying excavated soil when shield construction is performed in contaminated soil and shield excavator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which realizes more efficient purification processing and which can maintain favorable tunneling environment by effectively utilizing a shield machine itself in excavated soil purification processing when shield construction is performed in a contaminated soil.SOLUTION: A method for purifying the excavated soil when performing shield construction in the contaminated soil, includes a step of adding a purifier for the contaminated soil to a ground by a shield face, a step of stirring and mixing the excavated soil D1 taken inside a chamber 13 of the shield machine by a stirring means 14, and a step of transferring the stirred excavated soil inside the chamber to the outside of the chamber. If the contaminated soil contains a volatile organic compound, an ultrafine iron powder solution and a fine powder activated carbon solution are used as the purifier.

Description

  The present invention relates to a method for cleaning excavated soil and a shield excavator for shield excavation in soil contaminated with volatile organic compounds.

  As a purification technique for soil contaminated with volatile organic compounds (VOC), there is a technique of adding iron powder, activated carbon or the like to contaminated soil. Iron powder purifies VOC by chemical treatment (detoxification by reductive decomposition), and activated carbon adsorbs and immobilizes VOC by physical treatment (insolubilization by adsorption). This iron powder and activated carbon are used for in-situ purification of contaminated soil on the ground surface.

  When the excavated soil in the shield work is contaminated with VOC, it was purified by adding iron powder in a ground sediment pit or the like, or VOC was vaporized by thermal heat treatment and adsorbed on activated carbon.

  Patent Document 1 describes a technique that achieves both purification of VOC-contaminated ground and restoration of ground strength regardless of the type of solidifying material added to the metal-based reducing agent.

JP 2006-88110 A

The conventional purification techniques as described above have the following problems.
(1) Conventionally, since VOC treatment is performed on the ground part such as earth and sand pits, when the excavated soil is transported by a belt conveyor or a scrap steel car in the mud pressure shield method, VOC is vaporized in the shield mine and the mine environment is deteriorated. There is a problem to make. (In this respect, in the muddy water type shield method, the excavated soil is fluid transported in the pipe, so there is no risk of VOC vaporizing in the shield mine)
(2) Since it is necessary to carry out the earth and sand after confirming the completion of purification, when performing purification with iron powder etc. in the earth and sand pit as in the past, detoxification by reduction reaction takes several hours or more, There will be a waiting time for unloading the earth and sand (the earth and sand stock yard is required).
(3) Since the underground exhaust contains VOCs vaporized during sediment transport and purification in the soundproof house, a large-capacity ventilator with activated carbon is required.

  Therefore, the present invention can effectively use the shield excavator itself for the excavation soil purification process when the shield excavation is performed in the contaminated soil, thereby improving the efficiency of the purification process and maintaining a good underground environment. It is intended to provide excavated soil purification technology for shield excavation in contaminated soil.

  In order to solve the above problems, the present invention is a method for purifying excavated soil when shielded in the contaminated soil, the step of adding a cleaner for contaminated soil to the natural ground at the shield face, and a shield excavator And a step of stirring and mixing the excavated soil containing the cleaning agent taken into the chamber by a stirring means, and a step of transporting the agitated excavated soil in the chamber to the outside of the chamber.

  According to the present invention, a step of adding a contaminated soil purification agent to the natural ground at the shield face, a step of stirring and mixing the excavated soil containing the purification agent taken into the chamber of the shield excavator with stirring means, Since the agitated excavated soil in the chamber is transported to the outside of the chamber, the contaminated soil (contaminated ground) can be purified together with the shield excavator. Thereby, efficiency improvement of a contaminated soil purification process can be achieved. Moreover, the excavated soil containing the purification agent is stirred and mixed inside the sealed chamber, so that a good underground environment can be maintained.

  In this invention, when the said contaminated soil contains a volatile organic compound (VOC), it is desirable that the said purification | cleaning agent contains fine iron powder and fine powder activated carbon. In this way, safe and reliable VOC treatment can be performed efficiently and in a short time by the combined use of chemical treatment with fine iron powder (detoxification by reductive decomposition) + physical treatment with fine powdered activated carbon (adsorption / no need). be able to.

  In the present invention, in the step of adding the purification agent to the natural ground, it is desirable to add the purification agent in a liquid state. In the present invention, the purifier is added to the ground at the shield face and stirred and mixed in the chamber. Therefore, it is possible to perform efficient stirring and mixing when the purifier is made liquid. Moreover, when it is set as a liquid purification agent, the supply means can also cope with addition of a comparatively simple installation using a pump etc.

The present invention is a shield excavator used for excavation soil purification method when shield excavation in contaminated soil,
An excavator body equipped with a cutter for excavating natural ground at the tip,
A purification agent adding means for adding a contaminated soil purification agent to the face of the front surface of the excavator body,
The excavator body includes a chamber into which excavated soil containing a cleaning agent is taken in, a stirring unit that stirs the excavated soil in the chamber, and a transport unit that transports the stirred excavated soil.

  According to the shield excavator of the present invention, since the cleaning agent addition means for adding the cleaning agent for contaminated soil to the face of the excavator main body front is provided, the inside of the sealed chamber on the front surface of the excavator main body closest to the original position Contaminated soil treatment at can be performed. Further, in principle, it is only necessary to attach the purifier addition means to the existing shield excavator, and therefore, it is possible to cope with a low-cost method that effectively uses the existing shield excavator.

  In the present invention, the stirring means preferably includes a cutter, a rotary stirring blade, a fixed stirring blade, and an agitator. Thereby, the stirring efficiency of the excavated soil containing the purification agent can be sufficiently increased.

  In the present invention, the conveying means is preferably a screw conveyor. This is because in the case of a screw conveyor, the excavated soil stirred in the chamber can also be stirred by this screw conveyor.

  According to the present invention, the shield excavator itself can be effectively used for the excavation soil purification process when the shield is excavated in the contaminated soil, thereby improving the efficiency of the purification process and maintaining a good underground environment. It is possible to provide excavated soil purification technology for shield excavation in contaminated soil.

It is a schematic explanatory drawing which shows the excavation soil purification method which concerns on embodiment of this invention. It is typical explanatory drawing which shows the mechanism of the VOC process by the fine iron powder and fine powder activated carbon which concern on embodiment of this invention. It is a schematic process drawing which shows the excavation soil purification method which concerns on embodiment of this invention. It is a schematic process drawing which shows the excavation soil purification method which concerns on embodiment of this invention. It is a schematic process drawing which shows the excavation soil purification method which concerns on embodiment of this invention. It is a schematic process drawing which shows the excavation soil purification method which concerns on embodiment of this invention. It is a schematic process drawing which shows the excavation soil purification method which concerns on embodiment of this invention. It is a figure which shows the time-dependent change of the VOC gas concentration which concerns on embodiment of this invention. 1 is a schematic cross-sectional view of a shield excavator according to an embodiment of the present invention.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated with reference to drawings. However, although various technically preferable limitations for implementing the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

  FIG. 1 is an explanatory diagram schematically showing a method for purifying excavated soil when shielded excavation is performed in a contaminated soil according to the present embodiment, and FIGS. 2 (a) and 2 (b) are ultrafine iron powder and fine powder. Schematic diagrams showing the mechanism of VOC treatment with activated carbon, FIGS. 3 to 7 are process diagrams of the excavated soil purification method when shield excavation is performed in the contaminated soil. In these drawings, 10 is a mud pressure shield excavator, 20 is a purifier addition means (purifier supply device), 30 is a sediment pit, 40 is a soundproof house, 50 is a shield tunnel, and 51 is a shaft.

  The mud pressure shield excavator 10, as shown in FIG. 1, FIG. 3, etc., purifies contaminated soil on an excavator body 12 having a cutter 11 for excavating natural ground at the tip, and a face on the front surface of the excavator body 12. And a purifier addition means 20 for adding (injecting) the agent. The excavator main body 12 includes a chamber 13 into which the excavated soil D containing the cleaning agent is taken in, an agitating means 14 for agitating the excavated soil D in the chamber 13, and a conveying means 15 for conveying the agitated excavated soil D. ing. And the stirring means 14 becomes a structure stirred with the cutter 11, the stirring blade 16, the fixed stirring blade 17, the agitator 18, etc. FIG. That is, the cutter 11 also serves as a stirring means. Moreover, since the mud pressure shield excavator 10 is used, the conveyance means 15 is comprised with the screw conveyor.

  The purifier addition means 20 is a so-called purifier solution supply device, and includes a plurality of tanks, pipes, and a plurality of pumps. In the example shown in FIG. 1, a ground tank 21 and a mine tank 22 installed on the ground to accommodate the iron powder solution, a ground tank 23 and a mine tank 24 installed on the ground to accommodate the activated carbon solution, The pipes 25 and 26 and a pump P for feeding the activated carbon solution and the iron powder solution to the ground of the face through the pipes are provided.

  As a method of adding (injecting) these purifying agent solutions to the ground of the face, in this embodiment, a plurality of discharge ports (injection ports) for discharging the mud material toward the face of the face can be used. It is configured as follows. That is, the ends of the pipes 25 and 26 are connected to a supply pipe (not shown) of the mud material. In the drawing, among the plurality of discharge ports, a bubble material discharge port to be described later is indicated by a, an iron powder solution discharge port is indicated by b, and an activated carbon solution discharge port is indicated by c. These discharge ports are opened on the front face side of the cutter 11. In addition, in FIGS. 3 to 7, as a legend, the bubble material, the ultrafine iron powder, and the finely powdered activated carbon are indicated by different arrows. 3 to 7, (a) shows a state viewed from the front, and (b) shows a state viewed as a central longitudinal section.

  The mud pressure shield method is a method in which excavated soil is put into a mud state having plastic fluidity by pouring and mixing of mud materials and pressurized, and continuously excavated while maintaining the stability of the face. Therefore, in the VOC purification treatment method of the present embodiment, the function of the mud pressure shield method is utilized, and the fine iron powder (ultrafine iron powder) having a small particle size as well as the mud material (here, the bubble material) is used. ) And finely powdered activated carbon are used to uniformly stir and mix ultrafine iron powder and finely powdered activated carbon.

The VOC agitation treatment process in this mud pressure shield excavation is as follows.
(1) As shown in FIG. 3, the ground mass is scraped off by rotation of the cutter 11 at the face.
(2) At that time, a certain amount of foam material, ultrafine iron powder and finely powdered activated carbon are uniformly injected into the face according to the speed to plastically fluidize the excavated soil and start the VOC treatment.
(3) As shown in FIG. 4, as excavation progresses, excavated earth and sand D1 having plastic fluidity sequentially moves to chamber 13 filled with previously excavated earth and sand D.
(4) As shown in FIG. 5 and FIG. 6, in the chamber 13, further stirring and mixing are performed by rotation of the stirring blade 16 on the back of the cutter 11, rotation of the fixed stirring blade 17, and agitator 18, and the VOC process proceeds (several minutes after stirring). Will give you enough effect).
(5) As shown in FIG. 7, since the inside of the chamber 13 is full, the soil is discharged from the screw conveyor in a state where the VOC processing is finished in the order of excavation.

  As described above, excavated soil is a structure that continuously moves while stirring and mixing in the chamber 13, and at the stage of being excavated from the screw conveyor 15 after about 70 minutes on average after being excavated from excavation, The required VOC process is completed and does not adversely affect the underground environment.

Thus, in this embodiment, iron powder and activated carbon are added to the ground at the tip of the cutter of the shield excavator 10, agitated and mixed in the chamber 13 while advancing, and discharged from the screw conveyor 15. The VOC is not vaporized in the time up to (about 70 minutes).
Moreover, in order to suppress the volatilization of VOC in a short time, activated carbon is added simultaneously with the iron powder, and the VOC is not vaporized in a few minutes due to the adsorption effect of the activated carbon.
Furthermore, specially processed ultrafine particle type iron powder / fine powder activated carbon is dissolved in water and used as a solution so that it can be easily injected into the cutter tip of the shield excavator 10.

<Confirmation and response of the stirring and mixing state in the construction work>
In the implementation, the plastic fluidity in the chamber can be confirmed by the face pressure visualization system. As a result, when it is judged that the plastic fluidity such as solidification is partially poor and the mixture is not uniformly stirred and mixed, the additive material is additionally injected from the injection hole in the chamber, and the digging speed is reduced. It is also possible to take measures such as increasing the stirring time.

(A) About the certainty of the treatment effect regarding the difference in conditions between the laboratory test and the construction work The laboratory test (simulated and mixed with VOC contamination, φ0.3m Hobart mixer) and the construction work (in-situ VOC contamination soil, φ7.45m) In the mud pressure shield machine cutter rotation (stirring blade and back stirring blade), fixed stirring blade and agitator), (1) elution amount of VOC contaminated soil, (2) scale and time of stirring and mixing, (3) stirring There is a difference in the soil fullness, which is done.
About these differences, by the laboratory test shown in (B), the high-concentration VOC contaminated soil whose elution amount exceeds 100 times the standard specified by the Soil Contamination Countermeasures Law is stirred and mixed by a shield machine (filled in a sealed chamber). Even if the mixing time is shorter (30 seconds) than for a long time, vigorous stirring), it has been confirmed that it can be reliably processed in 3 minutes, so that even in the construction work, a reliable treatment effect can be obtained in a short time. There is no problem.

(B) Confirmation of reliable treatment effect by laboratory test VOC treatment methods using ultra fine iron powder and fine powder activated carbon are proven and reliable treatment methods, respectively, but can cope with the diversity of in-situ VOC contaminated soil, In addition, they are used in combination to ensure reliable processing in a short time. However, since there was no track record of processing with shield face conventionally, an indoor test was conducted, and it was confirmed from the results that there was no problem in the reliability of the processing effect as follows.
<Differences in conditions between laboratory tests and construction work>
In laboratory tests, high-concentration VOC pollution simulated soil (elution amount of trichlorethylene 2.8 mg / L) exceeding 100 times the standard specified by the Soil Contamination Countermeasures Law is used.
From the comparison of the laboratory test and the stirring and mixing of the shield machine, the stirring mechanism of the shield machine is 3.7 minutes of stirring and mixing, which is the same as the mixing and mixing of the laboratory test (30 seconds) (Table 1).

＜室内試験結果（図８参照）＞
超微細鉄粉と微粉末活性炭を添加・攪拌混合後3分でガス濃度はＶＯＣ作業環境管理濃度（10ppm）を満足する9ppmに低減する(鉄粉だけでは10ppmまで低減しない）。
その後も時間の経過に伴い、安定してガス濃度が低減する（添加・攪拌後50分で2.5ppm、活性炭だけでは濃度増減があり、安定して低減しない）。
公定法分析の結果、ＶＯＣ処理後ではトリクロロエチレン溶出量は0.064mg/Lであり、ＶＯＣ溶出量の低減率は97.7％である。
気泡材と併用しても、スランプロス、ＶＯＣ処理効果には問題はない。

<In-house test results (see Fig. 8)>
After 3 minutes after adding ultrafine iron powder and finely powdered activated carbon and mixing with stirring, the gas concentration is reduced to 9 ppm, which satisfies the VOC work environment management concentration (10 ppm) (not reduced to 10 ppm with iron powder alone).
After that, the gas concentration decreases stably over time (2.5 ppm in 50 minutes after addition / stirring, and the concentration increases and decreases only with activated carbon, and does not decrease stably).
As a result of official method analysis, after VOC treatment, the elution amount of trichlorethylene is 0.064 mg / L, and the reduction rate of the elution amount of VOC is 97.7%.
Even if it is used in combination with the foam material, there is no problem in the slump loss and the VOC treatment effect.

<Reliable treatment effect in a short time at the construction work based on the results of laboratory tests>
High concentration VOC contaminated soil (100 times the standard specified by the Soil Contamination Countermeasures Law) has a reduction effect that satisfies the work environment management concentration in 3 minutes. Since stirring and mixing can be performed in a strong and long time, the VOC treatment is completed at the time when the excavated earth and sand are discharged from the screw conveyor in the construction work, and the mine environment is not adversely affected.
Based on the reduction rate of VOC treatment (97.7%), the amount of elution after treatment of VOC-contaminated soil in the construction work (for example, when the maximum elution amount of trichlorethylene is 0.2 mg / L) can be estimated to be 0.0046 mg / L. It can be transported off-site as soil that satisfies the standard 0.03mg / L.

<In-chamber agitation (residence) time and VOC treatment effect>
(1) Basis of stirring (dwelling) time In the test example, the stirring (residence) time in the chamber means that the excavated earth and sand are discharged after 71 minutes. The basis for 71 minutes is the time calculated from the depth in the chamber for the digging speed at 20 mm / min.
Residence time in the chamber is 71 minutes (the excavated sediment is discharged after 71 minutes)
= (Chamber length 1430 mm) / (digging speed 20 mm / min) x = 1430/20 ≈ 71 min However, when the chamber capacity and the screw conveyor capacity considering the cutter spoke volume are taken into account, the result is as shown in FIG.
In this case, the average time from excavation to earth removal is 68.9 minutes = average passage time in the chamber is 64.4 minutes (stir mixing average time) + screw conveyor passage time is 4.5 minutes.

<Effect of VOC treatment during stirring (retention)>
In laboratory tests, it was confirmed that high-concentration VOC-contaminated soil, whose elution amount exceeds 100 times the standard specified by the Soil Contamination Countermeasures Law, can be reliably treated in 3 minutes. In the construction work, the time for the excavated sediment to pass through the chamber is thought to vary due to the stirring and mixing process in the chamber. In addition, if the passage time in the chamber is several minutes (3 minutes in the test) from the start of injection of finely powdered activated carbon, the VOC can be reliably processed.

  Therefore, according to the present invention, the effect in a short time and the characteristics of the mud pressure shield method (uniform mud mixing at the face, uniform stirring and mixing by rotating the cutter, etc., plastic fluidity filled in the chamber) The screw conveyor that performs efficient VOC processing by simultaneous excavation processing in the chamber without using another stirring time in the continuous shield excavation process. At the stage where the soil is discharged from the soil, it is possible to achieve a particularly remarkable effect that the processing is completed and the underground environment is not affected.

  The excavated soil purification technology according to the present invention can be applied to the case where a mud pressure shield excavator is used in addition to the mud pressure shield excavator.

DESCRIPTION OF SYMBOLS 10 Shield excavator 11 Cutter 12 Excavator main body 13 Chamber 14 Stirring means 15 Screw conveyor 16 Stirring blade 20 Purifier addition means (purifier supply device)
30 earth and sand bit 40 soundproof house 50 shield tunnel

Claims (6)

A method for purifying excavated soil when shield digging in contaminated soil,
Adding a soil cleaner with a shield face to the ground,
A step of stirring and mixing the excavated soil containing the purification agent taken into the chamber of the shield excavator with a stirring means;
Transporting the agitated excavated soil in the chamber out of the chamber;
A method for purifying excavated soil at the time of shield excavation in contaminated soil, characterized by comprising:   2. The excavated soil purification method for shield excavation in contaminated soil according to claim 1, wherein the contaminated soil contains a volatile organic compound, and the purification agent contains fine iron powder and fine powder activated carbon.   The method for purifying excavated soil when carrying out shield excavation in contaminated soil according to claim 1 or 2, wherein in the step of adding the purifier to the natural ground, the purifier is added in a liquid state. A shield excavator used for excavation soil purification method when shield excavation in contaminated soil,
An excavator body equipped with a cutter for excavating natural ground at the tip,
A purification agent adding means for adding a contaminated soil purification agent to the face of the front surface of the excavator body,
The excavator body includes a chamber into which excavated soil containing a cleaning agent is taken in, a stirring unit that stirs the excavated soil in the chamber, and a transport unit that transports the stirred excavated soil. Excavator.   The shield excavator according to claim 4, wherein the stirring means includes a cutter, a rotary stirring blade, a fixed stirring blade, and an agitator.   The shield excavator according to claim 4 or 5, wherein the conveying means is a screw conveyor.

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