JPH0132329B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method of creating a reclaimed land, in particular, dividing a certain area of the sea or a lake with a seawall, filling the divided area with soft mud, and then compacting it with sand. This invention relates to improved methods for handling and constructing soft mud, as well as methods for constructing sand, in a method for creating a reclaimed land that forms the ground.

Reclaimed land is created by reclaiming certain areas of oceans and lakes. This type of reclamation can be done by dumping industrial waste into a landfill area, but there is also a dredging method in which soil taken from the ocean floor, river bed, or lake bed is dumped into a landfill area. The method is also widely used.
In this case, if the sand on the seabed, riverbed, or lakebed is hard, a pump boat with a cutter is used to loosen it, and even if the loosened material is sucked up and thrown into the landfill area, its specific gravity is high. Because the soil naturally settles and accumulates more quickly, the formation of the ground occurs more quickly. Even when this is replaced by fine sand, it settles quickly and the ground can be formed quickly. However, although it is desirable to perform landfilling using only high-quality soil mixed with an appropriate amount of clayey soil, it is usually difficult in reality to secure a dumping site for clayey soil and perform landfilling using only high-quality soil. However, a large amount of soft mud is also used as landfill soil.

However, if this soft mud is extracted using a conventional pump-type dredger and placed in a landfill area, the soft mud fluidizes and becomes a slurry when the pump dredge sucks the soil. That is,
Soft mud is composed of silt, clay, and other colloidal sediments, which were originally suspended or floating in water and then settled and deposited over a long period of time. Consolidated over a long period of time, the mud particles are loosely bonded to each other, creating a structure that can be extracted as a lump. However, when a large force is applied to this clod, the loose bonds between the particles break down and the particles break apart, making the mud more likely to become fluid.

When this fluidized mud is introduced into a landfill area by a pump ship, the volume of the mud has expanded, for example, by several times, so that it occupies a large proportion of the landfill area, which reduces the volume of subsequent soft mud input. As a result, other soft mud cannot be added until the previously introduced soft mud has settled. Moreover, when such slurry water is poured into a landfill area, the mud particles are suspended in the water and do not easily settle, resulting in a significant slowdown in the rate of soil formation. It would take many years for this settled mud to have the same compacted structure as the mud that formed the original ground.

Therefore, in order to form a solid ground with this soft mud, a layer of sand with a high specific gravity is placed on top of the piled up soft mud, and this sand layer is used to press the soft mud layer, but in this case, the sand is blown out. Since this is often carried out in one place in the reclamation area, the blown out sand with a higher specific gravity may push the soft mud with a lower specific gravity to the upper layer, which not only requires the soft mud to settle again, but also creates a gap between the sand layer and the soft mud. There are places where the layers are reversed and it takes a long time to make the soft mud layer denser as mentioned above, and there are places where the soft mud and sand layers are uneven in thickness, and it takes a lot of effort to correct this. I end up spending a lot of time doing it.

In this way, the method of adding soft mud, letting it settle to the bottom of the water, and then compacting this soft mud with sand to form the ground takes, for example, one year to add soft mud. It takes several months for the mud to settle, and then several months to improve the ground with sand, making the construction process longer. If it takes time to prepare the reclaimed ground in this way, it not only results in poor work efficiency and a heavy burden on the construction contractor, but also delays the effective use of the reclaimed land, resulting in a large loss in terms of economic effects. Become.

In this case, even if you try to shorten the construction period by sucking up soft mud and sand at the same time using a pump ship and putting them into the landfill area together, only the sand with a higher specific gravity will settle first, and the surface layer of the reclaimed land will be formed by soft mud. As a result, the ground tends to be soft, making it unsuitable as a site for a heavy building, which is undesirable.

Furthermore, in the case of the conventional dredging and reclamation method, polluted water may flow out of the reclamation area along with drainage of surplus water, polluting the outside world, for example, the ocean.

Because of this, it is possible to immediately carry out ground improvement work with sand without allowing the soft mud to settle, and to move the soft mud to the landfill area without turning it into a slurry so as not to pollute the outside world. It is necessary to develop a method for creating a reclaimed land that can create a solid reclaimed land with a solid ground that does not cause the layer to reverse with the sand layer and also prevent soft mud and sand from being skewed and forming a reclaimed layer due to sand blowing out. It was wanted.

As described above, the present invention aims to improve the problems of the conventional method of reclaiming land using soft mud and compacting it with sand to create a reclaimed land. In addition, a layer of sand is layered on the soft mud layer by multi-point blowing to compact the soft mud layer, thereby improving the efficiency of the construction work of the reclaimed land. This made it possible to obtain reclaimed land with solid ground.

Next, one embodiment of the present invention will be described based on FIGS. 1 to 4.

Figure 1 shows the state in which soft mud from the ground that has already formed the ground on the seabed or river bed is taken out and loaded onto a cargo ship, in which a grab 1b installed at the tip of a crane 1a of a grab ship 1 is used. Soft mud a from the bottom of the water is collected without disturbing its structure, and this soft mud is loaded onto the earth transport vessel 2 by the rotation of the crane 1a. At this time, the soft mud is loaded onto the ship quietly so as not to disturb its structure. In this way, the soft mud is sequentially loaded into the soil transport vessel 2, and when the vessel is full, the vessel is moved to the reclamation area as shown in FIG.

The bottom of the moved earth carrier is opened and the loaded soft mud is dumped onto the water bottom. On this occasion,
Drop each lump of soft mud so that it falls naturally as quietly as possible. This process is carried out one after another in all parts of the landfill area, and the soft mud is spread everywhere so that there is no place where the soft mud will not be dumped. By repeating this process, the soft mud layer is gradually heaped up as much as possible by the soil transport vessel 2.

Then, as shown in FIG. 3, the sand b is sucked up by the pump ship 3 and is blown into the reclaimed area. That is, as shown in Fig. 3, a sand discharge pipe 5 is formed by connecting the pipes 4, 4, . The sand sucked up by the pump ship 3 is supplied to the sand pipe 6. In this way, the sand flows through the sand pipe 6 and is pushed out from its end. A part of this extruded sand leaks out from the gap between the sand pipe 6 and the adjacent pipe 4 at the end of the sand discharge pipe 5, and is scattered on the soft mud layer in the reclaimed area. In this way, the sand is blown off. On the other hand, the remaining part of the pushed out sand is sent to the next adjacent pipe 4, and as in the case above, a part of it leaks and is blown away, and the remaining part is further sent to the next adjacent pipe 4. sent to.
Thereafter, similar leakage blowing is performed from the gaps between other pipes as well.

Sand is sprayed in this way, and in order to spray sand to all parts of the reclaimed area, piping is installed as shown in FIG. 4. That is, the sand discharge pipes 5, 5... are branched and connected in parallel to the sand conveyance pipe 6 shown in FIG.
Sand discharge pipes 5a, 5 similar to this sand discharge pipe 5 are disposed on both sides of...
a..., 5b, 5b,... are provided in a branched manner. In addition,
7 is a seawall.

When sand is leaked and blown from such sand discharge pipes 5, 5..., 5a, 5a... and 5b, 5b..., sand may be scattered in the same manner as above throughout the area between the pipes 4 shown in Fig. 3. However, if you do this, the sand scattered from adjacent gaps may overlap and a large amount of sand may fall on top of the soft mud layer at once, and in this case, the relatively light soft mud may fall onto the upper layer due to the impact of the sand. As the sand gets wet, spray every other gap, and when the sand has completed one cycle, spray again in the opposite direction to the previous one. It is more preferable to do so. At this time, in the gaps where no leakage occurs, the flanges of adjacent pipes may be brought into close contact with each other and bolted.

When sand is sprinkled on the soft mud layer as described above,
Since the sand particles fall into the soft mud layer in pieces, they do not kick up the soft mud, and since sand has a higher specific gravity than the soft mud, they penetrate between the lumps of soft mud and into the soft mud, displacing that much water. This expelled water rises through the gaps in the sand by capillary action and is removed. In this way, the structure of the soft mud becomes denser, and the sand is bound together by the sticky soft mud component, making the soft mud layer stronger.

Next, another embodiment shown in FIGS. 5 and 6 will be described.

FIG. 5 shows the installation state of the pipes 5', in which the reclaimed area is divided into small areas by the grid-shaped pipes 5', and sand is blown out for each section. The piping of each section is provided with an interval of 50 to 150 m between opposing sides, for example.
With this kind of piping, if sand is blown out at multiple points as shown in Figure 3, large sand particles tend to accumulate closer to the point where they are blown out due to their faster settling speed, as shown in Figure 6. , the sand that settles slowly due to the slope will accumulate in the far direction. As the sand continues to be blown out, the tips of the sand piles extend farther away, and the tips of the sand piles blown out from the blowout points on opposite sides of the pipe approach each other in the shape of an inverted oblate square pyramid. A deposited layer is formed that forms the recesses. The depressions in this sedimentary layer are then smoothed out with the surrounding sand to create a developed area. Note that 5'a is a receiving frame.

Forming the reclaimed ground in this way not only saves on piping, but also consolidates the soft mud at the bottom. For example, in the case where the sand deposit layer at the sand blowout point above the soft mud layer is 2.5 m long and the tip of the deposit layer extends 25 meters away, the degree of this consolidation is determined by The soft mud at the tip has a water content of 50 to 60% of the solid content, respectively.
60 to 80% and 70 to 90%, making the structure of the soft mud more dense compared to the original rock where the soft mud was taken out before it was laid down, where the water content was 100% relative to the solid content. I have to.

Note that although the piping is arranged in a grid pattern in Figure 5,
As shown in Figures 8 and 9, subdivisions of the reclaimed area may be divided by parallel pipes 5'', U-shaped pipes 5, and orthogonal pipes 5''''.

According to the present invention, soft mud is poured into a landfill area without disturbing its structure to form a soft mud layer, and a layer of sand is further formed on top of this soft mud layer by multi-point blowing. There is no leakage to the outside world,
Not only can the formation speed of the soft mud layer be increased, but also the strength of the ground can be increased. This will improve the efficiency of the landfill work and shorten the construction period. In particular, compared to the conventional method of creating a reclaimed land by dredging, not only is there no need for a period for settling soft mud, but the soft mud layer that forms the ground retains the consolidated structure of the original ground, which was not the case. The construction period for consolidation with sand, such as
After the soft mud layer is formed, the period for consolidation with sand, that is, the period for ground improvement work, which conventionally required six months, can be shortened to, for example, one month. As a result, the reduction in the construction period required for mud settling in the conventional method and the reduction in the construction period for ground improvement using this sand means that if the construction period for the conventional method of creating a dredged and reclaimed land is, for example, two years, approximately This means that the landfill can be created in half the time, 13 months.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a part of the apparatus used in one embodiment of the method of the present invention, FIG. 2 is an explanatory diagram of another part of the apparatus, and FIG. 3 is an explanatory diagram of still another part. , FIG. 4 is an explanatory plan view showing a specific example of the arrangement of the sand feeding pipe and sand discharge pipe shown in FIG. 3, FIG. 5 is a diagram corresponding to FIG. 4 in another embodiment, and FIG. An explanatory diagram corresponding to FIG. 2 of the ground formation process in the embodiment, and FIGS. 7 to 9 are diagrams corresponding to FIG. 4 in other embodiments, respectively. In the figure, 1 is a grab ship, 2 is an earth carrier, 3 is a pump ship, 5, 5a, 5b, 5', 5'', 5, 5''''' is a sand pipe, a is soft mud, and b is sand. It is.

Claims (1)

[Claims] 1. Collecting the compacted soft mud that forms the ground at the bottom of the water as soil clods without disturbing them, loading the soil clods onto an earth transport ship without disturbing them, and reclamation of the loaded soil clods. A layer of soft mud with a uniform thickness is formed by gently pouring sand into the area, and a multi-point sand blowing device is installed above the soft mud layer to blow sand at multiple points. A method of creating a reclaimed land characterized by forming the ground by depositing layers and compacting them. 2. The multi-point sand blowing device is composed of sand discharge pipes that blow sand from multiple locations spaced apart, and the sand discharge pipes are piped to divide the reclaimed area into small areas, and the intervals between the pipes are set by the opposing sand discharge pipes. 2. The method of creating a reclaimed land according to claim 1, wherein the sand is provided so that when the sand is blown out, the tips of the sand piles overlap or are in contact with each other.