JPS6411765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a landfill method for filling soft mud with a high water content (hereinafter referred to as sludge) in a coastal landfill using a pump dredger or the like.

If the sludge that has accumulated on the seabed is dredged using a pump dredger, etc., and the sludge sucked up along with the water is thrown into a planned reclamation site that has divided the nearby sea area to create a reclaimed land, the reclaimed land will be extremely soft. becomes the ground, and in order to use it as land,
Naturally, the ground must be improved.

Therefore, as one of the conventional ground improvement methods, there is a method as shown in Fig. 1. This method involves laying sand 2 on the seabed 1 in a reclaimed land, laying a drainage pipe 3 in the sand, and then anchoring a rope drain 4, which is a type of vertical drain used for improving soft ground, at the tip of the pipe. The upper end of the rope drain 4 is connected to the float 6 so that the entire rope drain 4 is held vertically, and then the sludge 7 is poured into the litter 2 together with water using a pump or the like. After creating a landfill, connect a vacuum pump to the drainage pipe 3 through an appropriate pipe, and operate the vacuum pump to drain the moisture in the sludge 7 to the rope drain 4, the litter 2, and the drainage pipe. The reclaimed ground is improved by dewatering through three steps in sequence.

However, the conventional method has drawbacks such as difficulty in maintaining the rope drain 4 vertically because the rope drain 4 moves due to flowing sludge and water flow during the reclamation work of the sludge 7.

The object of the present invention is to obtain a reclamation method that eliminates these drawbacks.

The reclamation method of the present invention includes a step of arranging a flexible drainage pipe on the seabed, a step of providing a drainage pipe communicating with the flexible drainage pipe via a drainage mechanism, and a step of installing a drainage pipe between the flexible drainage pipes. A step of applying sand, a step of pouring sludge onto the sand to form a primary fill layer, and driving a drain into the sand through the primary fill layer so that the head of the drain is within the primary fill layer. a step of activating the drainage mechanism; a step of further injecting sludge onto the primary reclamation layer to form a secondary reclamation layer; It is characterized by the process of covering the soil.

Embodiments of the present invention will be described below with reference to the drawings.

In the present invention, first, as shown in FIGS. 2 and 3, one end of the flexible drainage pipe 8, which is floating on the sea using a buoy or the like, is sequentially sunk from the sea to the seabed. A network of flexible drainage pipes will be placed on top. The flexible drain pipe is a pipe whose surface is made of a plastic coil and covered with a coarse canvas, and is similar to a so-called drain hose that is conventionally used for the purpose of draining water near the ground surface.

Next, a drainage pump 10 is arranged on the seawall 9 side, and its water suction side is connected to one end of the flexible drainage pipe 8. A drainage pipe 11, whose lower end is connected to the drainage side of the drainage pump 10, is connected to the seawall 9. The flexible drainage pipes 8 are installed using the pipes 8, and the bedding 2 is applied between the flexible drainage pipes 8. After the construction of the sand bed 2, sludge is poured onto it using a pump dredger to form a primary reclaimed layer 12. The primary reclaimed layer 12 is constructed so that its upper surface is approximately 3 m below sea level. Next, a stirring blade 13 is provided on its outer circumferential surface, and a vertical drain 14 made of a plastic board drain, that is, a strip-shaped core material made of synthetic resin and water-permeable nonwoven fabric pasted on both sides, is inserted into the inside of the blade, and the bottom end of the vertical drain 14 is inserted. A mandrel 15 equipped with a cone 16 is driven into the sand bed 2 through the primary fill layer 12. Here, the upper end of the drain 14 is submerged by about 1 m into the primary landfill layer 12, and then the drainage pump 10 is operated to remove moisture in the primary landfill layer 12 from the drain 14, litter 2, and flexible drainage pipe 8. , the water is drained through the drain pipe 11.

In addition, since the upper end of the drain 14 is sufficiently buried in the primary landfill layer 12, when the drain pump 10 is operated, the water level lowering and negative pressure effects in the primary landfill layer 12 are promoted. The increase in consolidation load (effective stress) is also significantly promoted, and as a result, the improvement effect is further promoted. If the drainage pump 10 is operated for a certain period of time, the primary landfill layer 1
2 is consolidated and its volume decreases, the operation of the drainage pump 10 is stopped and sludge is again injected onto the primary reclaimed layer 12 by a pump ship to form a secondary reclaimed layer 17, and furthermore, sandy soil 18 is placed on top of it. Cover it. In the above process, the secondary landfill layer 17 may be constructed while the drainage pump 10 continues to operate.

Since the construction method of the present invention is as described above, it has the following advantages.

(a) In the conventional construction method, sludge mud with a high velocity is pumped between the drains that are lined up in the water, making it difficult to hold the drains and also causing problems with the piping of the sand discharge pipe for introducing the mud. However, in the present invention, the drains are installed after the primary reclamation, which solves the problems encountered in conventional construction methods.

(b) After installing the vertical drain 14 in the primary landfill layer 12 made of sludge, the primary landfill layer 1
Since the volume of 2 is reduced, it is possible to construct a secondary landfill layer 17 made of sludge that increases accordingly. Therefore, compared to conventional methods, the amount of sludge that can be disposed of in the limited volume of the landfill can be increased.

(c) When installing the vertical drain 14 in the primary landfill layer 12 made of sludge, the upper end of the vertical drain 14 is buried in the primary landfill layer, so the drain pipe 11 is drained immediately after the vertical drain 14 is constructed. The drainage effect is good when the pump 10 is operated.

(d) Flexible drainage pipes are arranged in a network on the bottom of the water throughout the entire area of the landfill, sand is placed between the arranged flexible drainage pipes, and one end of the flexible drainage pipes is placed close to the seawall. This allows the drainage pipe to be placed near the seawall. Therefore, there is no need to install drainage equipment such as a drainage pipe in a landfill with poor footing.

(e) Normally, when the sea surface is filled with sludge by a pump ship, the sludge forms floes and sinks, so the volume of the accumulated sludge increases due to the formation of a skeleton by the floes (fluff structure). Therefore, if the skeleton is disturbed to the point where it is destroyed, the soil structure becomes lower and the volume decreases, causing subsidence.

In the method of the present invention, after the primary reclamation is completed, a mandrel 15 with disturbance blades 13 is inserted from the barge and a drain 14 is driven into the bottom drainage sand layer. After settling, the amount of reclaimed soil can be increased.

(f) Since the reclaimed ground has been considerably improved before it is covered with sandy soil as the final step of the method of the present invention, it is possible to plan for early use of the reclaimed ground.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the conventional construction method, Figure 2 is a plan view showing the arrangement of flexible drainage pipes etc. used in the construction method of the present invention, Figure 3 is a sectional view explaining the construction method of the present invention, and Figure 4 is a diagram illustrating the construction method of the present invention.
The figure is a front view of the lower part of the mandrel used in the construction method of the present invention, and FIG. 5 is a cross-sectional view thereof. 1... Seabed, 2... Sand, 3... Drainage pipe,
4... Rope drain, 5... Anchor, 6...
Float, 7... Landfill sludge, 8... Flexible drainage pipe, 9... Seawall, 10... Drainage pump, 1
1...Drainage pipe, 12...Primary landfill layer, 13...
... Disturber blade, 14... Vertical drain, 15... Mandrel, 16... Cone, 17... Secondary reclaimed layer,
18...Sandy soil.

Claims (1)

[Claims] 1. A process of arranging a flexible drainage pipe on the seabed, a process of providing a drainage pipe that communicates with the flexible drainage pipe via a drainage mechanism, and a process of applying sand between the flexible drainage pipes. a step of injecting sludge onto the litter to form a primary fill layer; and a step of driving a drain into the litter through the primary fill layer so that the head of the drain is buried in the primary fill layer. a step of activating the drainage mechanism; a step of further injecting sludge onto the primary reclaimed layer to form a secondary reclaimed layer; and a step of covering the secondary reclaimed layer with sandy soil. A land reclamation method characterized by the following.