JP4085378B2 - Bottom mud covering method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating bottom mud of the ocean, lakes, rivers and the like, and more particularly to a bottom mud covering method suitable for containment of soft polluted bottom soil containing harmful substances such as dioxin.
[0002]
[Prior art]
Various methods such as dredging, reforming, replacement, sand covering, etc. have been used as methods for treating the bottom mud of oceans, lakes, rivers, etc., but without requiring large-scale equipment for construction. In addition, since a complicated post-treatment is not required, the sand covering method tends to be frequently used.
By the way, if the bottom mud is a soft polluted bottom soil containing toxic substances such as dioxin, simply spreading sand on this will cause the bottom soil (bottom mud) to rise and diffuse around. , Will cause new pollution. In addition, it is unavoidable to stir and mix contaminated sediment and sand, so it is difficult to obtain high-quality sand because it is necessary to form a thick sand-capping layer to suppress the outflow of pollutants such as dioxin. As a result, the cost burden for bottom mud treatment becomes extremely large.
[0003]
Therefore, for example, in the construction method described in Patent Document 1, a device that can quantitatively discharge sand by rotation of a rotary discharge valve is attached to the tip of a sand discharge pipe that extends from the top of a trolley to the vicinity of the bottom of the water. In the construction method described in Patent Document 2, a water bottom spraying device in which a reducing plate is arranged under the hopper with a water injection pipe is installed near the water bottom. The sand that has fallen on the pressure-reducing plate is distributed as it breaks down with the water discharged from the water injection pipe.
In Patent Document 3, a water permeable material such as sand and crushed stone is deposited on the sludge layer to form a water permeable layer, and then an impermeable sheet is laid on the water permeable layer. In addition, a bottom mud treatment method is described in which a solidifying material such as mortar is deposited, and then the sludge layer is forcibly drained through the water-permeable layer.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-197465 [Patent Document 2]
Japanese Patent Laid-Open No. 11-256579 [Patent Document 3]
Japanese Patent Application Laid-Open No. 51-90732
[Problems to be solved by the invention]
However, according to the sand-capping method described in Patent Documents 1 and 2 and the like, since sand is distributed near the bottom of the water, although the rise of soft contaminated sediment is suppressed, sand and contaminated sediment Stirring and mixing cannot be avoided, and the essential problem cannot be solved. In particular, it is difficult to predict how thick the agitated mixed layer of sand and contaminated sediment will be formed, and it is necessary to form a thick sand covering layer for safety reasons, which increases the cost burden. Inevitable.
In addition, according to the construction method described in Patent Document 3, since the water-permeable layer (covered sand layer) is covered with the water-impermeable sheet, there is no special problem even if sand and contaminated sediment are mixed, but the sheet is laid. In addition to the necessity of joining (welding) the seams of sheets having a predetermined width, the periphery of the sheets must be completely fixed to the bottom of the water, and the sheets themselves are significantly more expensive than general-purpose civil engineering sheets. Therefore, a great deal of cost is required for laying the sheet.
The present invention has been made in view of the above-described conventional problems, and the problem is that a thick soil covering material is deposited without causing the bottom mud to rise, and an expensive water-impermeable sheet is provided. An object of the present invention is to provide a bottom mud covering method capable of reliably containing bottom mud containing harmful substances without using it.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a bottom mud covering earth construction method in which a water-permeable civil engineering sheet is laid on the bottom of the water to cover soft bottom mud and then a slurry covering material is deposited on the civil engineering sheet. The soil covering material contains 20% by weight or more of fine particles having a particle size of 74 μm or less, and the soil covering material is at least one selected from mountain soil, construction residual soil, coal ash, blast furnace slag, and sewage sludge molten slag. There use, characterized in that for discharging a slurry of said cover soil material from a discharge pipe which gave the equipped with backhoe working ship.
In the bottom mud covering method, the civil engineering sheet is laid first, and then the earth covering material is deposited on the civil engineering sheet, so that the bottom mud does not soar, and the bottom mud and the earth covering material And will not mix. Moreover, as a result of preventing mixing of the bottom mud and the soil covering material, the thickness of the soil covering layer can be reduced.
In addition, since the soil covering material contains 20% by weight or more of fine particles having a particle size of 74 μm or less, even if the moisture that has passed through the water-permeable civil engineering sheet contains a harmful substance such as dioxin, Hazardous substances are adsorbed on the granule and the outflow of harmful substances is more reliably prevented.
Furthermore, since at least one selected from coal ash, blast furnace slag, and activated sludge molten slag is used as the above-mentioned soil covering material as well as mountain soil and construction residual soil, it is significantly cheaper than sand.
In the present invention, a non-separation material (separation preventing material) may be added to the above-mentioned soil covering material. In this case, since material separation is reliably prevented, the soil covering material is efficiently deposited on the civil engineering sheet. Can be made. Examples of such non-separating materials include polyacrylamide, but since coal ash also functions as non-separating material, no special non-separating material is required when coal ash is used as a covering material.
In the present invention, the slurried covering material preferably has a slump of 8 to 20 cm. By setting the slump in this way, the fluidity is improved, and the covering material can be transported efficiently over a long distance, and can be smoothly pumped to just above the civil engineering sheet.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
In the present embodiment, the bottom mud in the harbor is contained. In implementing this, first, as shown in FIG. 2, a work ship (seat laying) in which a crawler crane 2 as a work machine is mounted in the vicinity of the quay 1. Ship) 3 is moored, the crane 2a of the crawler crane 2 is operated, and the permeable civil engineering sheet 4 is placed on the soft polluted bottom soil layer (bottom mud layer) B accumulated on the seabed ground (water bottom) A. This operation is repeated while moving the crawler crane 2 and moving the sheet laying ship 3 to lay the civil engineering sheet 4 in the necessary range in the harbor.
Next, instead of the sheet laying ship 3 as shown in FIGS. 1, 3 and 4, a work ship (covering ship) 11 equipped with a backhoe 10 as a work machine is moored in the vicinity of the quay 1, The backhoe 10 is run on the earthen vessel 11 to deposit the slurryed earthen material on the civil engineering sheet 4, and this operation is repeated while moving the earthen vessel 11, so that the desired thickness is obtained on the earth engineering sheet 4. The soil covering layer C is formed.
[0008]
Although the construction method for laying the civil engineering sheet 4 is arbitrary, the sheet laying construction method described in Japanese Patent No. 3108802 is adopted here. In this construction method, a sheet roll formed by winding the civil engineering sheet 4 is supported by a hanging tool 5 suspended from the crane 2a of the crawler crane 2. The position of the hanger 5 is monitored on the seat laying ship 3 by GPS and an ultrasonic surveying system, and the seat laying ship 3 is positioned and operated by a winch 7 for operating the wire 6. The In FIG. 2, 8 is a control room equipped with an external GPS antenna 8a and various control devices (not shown) inside, and the operations of the crawler crane 2 and winch 7 are concentrated in this control room 8. Controlled. In addition, an underwater camera 9 that monitors the laying state of the civil engineering sheet 4 is installed in the hanging tool 5.
[0009]
In laying the sheet, after fixing one end of the civil engineering sheet 4 using the weight W, the crane 2a of the crawler crane 2 is operated while confirming the position of the hanging tool 5 to remove the hanging tool 5 from the contaminated sediment. Move along layer B. Then, the civil engineering sheet 4 is pulled out from the sheet roll at a constant speed, and the contaminated sediment soil layer B is gradually covered with the civil engineering sheet. At this time, the civil engineering sheet 4 quietly settles on the contaminated bottom soil layer B, and therefore the contaminated bottom soil does not rise. Then, after laying the civil engineering sheet 4 corresponding to the total amount of the sheet roll, a new sheet roll is set on the hanging tool 5, the position of the crawler crane 2 is changed, and the civil engineering sheet 4 previously laid is wrapped. Then, the next civil engineering sheet 4 is laid, and then the above operation is repeated while moving the sheet laying ship 3 at a predetermined pitch, thereby laying the civil engineering sheet 4 in the necessary range.
[0010]
The method of depositing the slurry covering material on the civil engineering sheet 4 to form the covering layer C is arbitrary, but here, the discharge pipe is provided at the tip of the arm 10a of the backhoe 10 disposed on the covering vessel 11. 12, a hopper 13 for storing slurry covering material on the soil covering ship 11 and a pump 14 are mounted, and the slurry covering material in the hopper 13 is piped to the discharge pipe 12 by operating the pump 14. 15 is pumped. In the present embodiment, the slurry covering material is prepared by a mixing plant (not shown) installed on land, and the covering material slurried by this preparation is extended from the land to the covering vessel 11. Pumped to the hopper 13 through the transport pipe 16. It is to be noted that the soil covering ship 11 is operated and moored by the operation of the wire 18 by the winch 17 mounted thereon. The discharge pipe 12 is provided with an underwater camera 19 for monitoring the soil covering condition.
[0011]
In the above mixing plant, an appropriate amount of water is mixed with mountain soil, construction residual soil, coal ash, blast furnace slag, activated sludge molten slag, etc. prepared as a covering material, and a solidified material, an unseparated material, etc. are further added as desired. Turn into. In the present embodiment, as the covering material, a material containing 20% by weight or more of fine particles having a particle size of 74 μm or less is used. For this reason, about the earth covering material to be used, the particle size addition curve is calculated | required beforehand, content of a fine grain part is grasped | ascertained, and the compounding quantity of various earth covering materials is determined as needed. Moreover, in this Embodiment, the compounding quantity of water is adjusted suitably and the slump of the slurry covering material is adjusted to 8-20 cm. In addition, when adding a solidification material and a non-separation material, those addition amounts may be slight.
[0012]
When depositing the slurry covering material on the civil engineering sheet 4, the discharge pipe 12 provided on the backhoe 10 is brought close to the civil engineering sheet 4, and the backhoe 10 is reciprocated in the ship width direction while maintaining its height. (FIG. 4) Alternatively, the arm 10a is operated, and during this time, the slurry covering material is pumped from the pump 14 to the discharge pipe 12. Then, the covering material discharged from the discharge pipe 12 accumulates on the civil engineering sheet 4 in accordance with the travel or arm operation of the backhoe 10, and the backhoe 10 moves back and forth while moving the covering vessel 11 at a constant pitch. By repeating the operation, the soil covering layer C having a predetermined thickness is formed on the civil engineering sheet 4. In this case, the soil covering layer C may be formed in one layer, but may be formed in multiple layers to have a required thickness. In the case of forming in multiple layers, since the discharge amount of the slurry covering material from the discharge pipe 12 can be reduced, the diffusion of the covering material is suppressed. The discharge amount of the soil covering material from the discharge pipe 12 can be controlled by adjusting the pumping pressure from the pump 14 to the discharge pipe 12, the traveling speed of the backhoe 10, and the arm operation speed.
[0013]
In this way, the polluted bottom soil layer B having a soft bottom is double-contained by the permeable civil engineering sheet 4 and the overlying soil layer C, and dioxins contained in the contaminated bottom soil layer B, etc. No harmful substances will flow out. In this case, since the water-permeable civil engineering sheet 4 is significantly cheaper than the water-impermeable sheet, the construction cost does not increase so much. In the present embodiment, mountain soil, construction residual soil, coal ash, blast furnace slag, activated sludge molten slag, and the like are used as the covering material, so that the construction cost is reduced as compared with the case where expensive sand is used. Particularly, construction waste soil, coal ash, blast furnace slag, activated sludge melted slag, etc. are generated in large quantities as waste, which is extremely useful for waste disposal. In the present embodiment, in particular, as the soil covering material, a material containing 20% by weight or more of fine particles having a particle size of 74 μm or less is used. Even if it is contained, harmful substances are adsorbed on the fine particles, and the outflow of harmful substances is more reliably prevented.
[0014]
In the above embodiment, was used crawler crane 2 as a working machine of the sheet laying, the type of the working machine is optional, it may be used cash forte other work machine crawler crane 2 Of course.
Moreover, in the said embodiment, although the mixing plant was installed on land and the slurry covering material slurried to the hopper 13 on the covering vessel 11 was pumped, this mixing plant was installed on the covering vessel 11 If it is installed on the soil covering ship 11, the contents of the preparation can be quickly changed while observing the soil covering condition.
In the above embodiment, the slump of the slurry covering material is set to 8 to 20 cm, but the present invention may set the slump smaller, and when the slump is set small, In addition to being able to be transported by a conveyor, it is also possible to place a covering material using a tremy tube.
[0015]
【The invention's effect】
As described above in detail, according to the bottom mud covering earth construction method according to the present invention, a permeable earthwork sheet is laid on the bottom mud, and then the covering material is deposited on the earthwork sheet. not only will not be increased, also eliminates mixing and the mud and soil covering material can contain reliably even sediment when the thickness of the soil cover layer. Further, since the soil covering material contains 20% by weight or more of fine particles having a particle size of 74 μm or less, even if the moisture that has passed through the permeable civil engineering sheet contains a harmful substance such as dioxin, the fine particles Hazardous substances are adsorbed to the minute and the outflow of harmful substances is more reliably prevented. Moreover, in addition to the use of inexpensive civil engineering sheets , waste such as mountain soil and construction surplus soil is used as the covering material , so that construction costs can be reduced and the utility value of the present invention is great. is there.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view showing a covering situation of soil covering in the bottom mud covering method according to the present invention.
FIG. 2 is a cross-sectional view showing the overall construction status of sheet laying in the bottom mud covering method.
FIG. 3 is a cross-sectional view showing an overall construction situation of soil covering in the bottom mud covering method.
FIG. 4 is a plan view showing an overall construction situation of soil covering in the bottom mud covering method.
[Explanation of symbols]
2 Crawler crane (work machine)
3 Sheet laying ship 4 Permeable civil engineering sheet 10 Backhoe (work machine)
11 Covering vessel 12 Discharge pipe 13 Hopper 14 Pump A Submarine ground (water bottom)
B Contaminated sediment layer (bottom mud)
C Soil cover layer

Claims (3)

In the bottom mud-covering method in which a water-permeable civil engineering sheet is laid on the bottom of the water and covered with soft bottom mud, a slurry covering material is deposited on the civil engineering sheet. includes a particle content of 20 wt% or more, as said cover soil material, Yamado, construction waste soil, have use coal ash, blast furnace slag, at least one selected from sewage sludge slag, work ship slurry said cover soil material The bottom mud-covering method is characterized by discharging from the discharge pipe attached to the backhoe mounted on the top . The soil covering material, mud soil cover method according to claim 1, characterized in that the addition of nondisjunction material.   The bottom mud covering method according to claim 1 or 2, wherein a slump of the slurry covering material is set to 8 to 20 cm.

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