JP2003261929A - Volume reducing method for water bottom soft ground - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a volume reducing method for water bottom soft ground capable of ecomonically carrying out a descending work of the water bottom face for securing water depth of a route by making use of water bottom soft ground consolidation method. <P>SOLUTION: An impervious caisson body 1 having a vertically cylindrical impervious wall 1a piercing into the ground at the periphery, closed at the top 1b and opened at the lower end, is used. A plurality of drain pile driving sections 10 having a unit area corresponding to the size of the impervious caisson 1 are set with a distance a wider than a vertical drain member distance b at the surface of the water bottom soft ground. A number of vertical drain piles 12, 12, etc., are driven from the water bottom soft ground surface at every drain pile driving section 10, and a horizontal drain material 13a tied to the vertical drain material is laid in the water bottom soft ground surface, the impervious caisson body 1 is put on to cover the upper face of the material 13a by making the impervious wall 1a penetrate the soft ground. After that, the inside of the horizontal drain material 13a in each impervious caisson body is vacuumized at the same time to dewater the water bottom soft ground and reduce the volume. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a volume-reducing method for soft-bottom soft ground to reduce the depth of the soft-bottom soft ground such as rivers, lakes and marshes so as to increase the water depth for securing routes.

[0002]

2. Description of the Related Art Conventionally, dredging has been carried out as a construction for making a water depth shallower than a certain depth where soft soil such as sludge has accumulated on the bottom of the water.
For this type of dredging, there are a method of excavating and excavating the bottom sediment by a bucket elevator, a method of excavating the bottom of the soil with an excavation blade, and a suction of the excavated soil with water by a pump. It is sent to the dredged soil treatment pond for landfill treatment.

Further, the volume of the soft ground at the bottom of the water can be reduced by subjecting the soft ground to dehydration treatment.
When constructing a water-bottom structure, various types of water-bottom soft-ground consolidation methods have been developed for consolidating the soft foundation of the water bottom and exerting the strength required as a foundation.

As a conventional water-bed soft ground consolidation method, for example, as disclosed in Japanese Patent No. 2840908,
Vertical drains are placed at equal intervals in the soft ground at the bottom of the water, and horizontal drains such as sand are installed on the ground surface continuously from the upper end of each vertical drain, the surface is covered with a water-blocking material, and the inside is drained. A method has been proposed in which the pump is drained to reduce the pressure and the vertical drain is used to reduce the pressure inside the soft ground to consolidate. As a water blocking material,
In addition to a box body of which the lower end is open and the lower end is open, a sheet-shaped member is also proposed.

[0005]

The above-mentioned conventional method for securing the depth of the channel by dredging requires an area for the treatment of dredged soil, but in recent years, most of the landfill area for the treatment of dredged soil is used. It was often exhausted and a new landfill area could not be secured, and there was a problem that dredging work could not be performed due to the problem of dredged soil treatment.

Further, since the above-mentioned conventional method for consolidating soft-bed soft ground is based on the premise that its purpose is to use it as foundation ground, etc., the drain material is uniformly placed over the entire area of the improved ground. , It is designed to generate uniform proof stress over the entire destination ground. For this reason, the intervals of the vertical drain materials to be placed in the destination ground are set to be uniform over the entire area.

[0007] In most cases, the conventional water-bed soft ground consolidation method builds a structure on the ground after consolidation, and lowers the ground surface in order to secure the water depth necessary for the navigation route. It has not been used for this purpose, and it was economically disadvantageous to carry out the conventional water-bed soft ground consolidation method to secure the water depth.

The present invention has been made in view of such conventional problems.
Even if it is difficult to secure a dredged soil treatment area by using the water soft soil consolidation method, it is possible to economically perform work to lower the water floor to secure the water depth of the channel, etc. The purpose was to provide a chemical method.

[0009]

[Means for Solving the Problems] A feature of the volume-reducing construction method for a water-bed soft ground according to the present invention for solving the above-mentioned conventional problems and achieving an intended object is that a vertical tubular shape is provided around the circumference. Using the open bottom type impermeable enclosure with a watertight impermeable wall of which the top is closed, and the wide bottom that fits the size of the impermeable enclosure on the surface of the soft ground A plurality of drain material driving sections are set at intervals wider than the vertical drain material spacing in the drain material driving section, and for each of the drain material driving sections, from the water bottom soft ground surface. A large number of vertical drain materials are placed and horizontal drain materials that are continuous with the vertical drain materials are installed on the surface of the water bottom soft ground, and the impermeable box body is placed in a position to cover the upper surface thereof, and the soil penetrating impermeable wall. The soft ground to cover it, and after that, install each side by side. By vacuum Mizuhako body horizontal drain material in the same time is to iodide reduced by performing the dehydration in the sea bed soft ground.

In the above-mentioned construction method, the space between the water-blocking boxes is adjusted according to the distance between the water-blocking boxes between the adjacent draining material-placing sections according to the subsidence of the water-bottom soft ground surface caused by the dehydration of the sections. The length of the water is settled, and the water collecting well installed on the bottom of the water is communicated with the water shield box through the drainage pipe, and the water is drained from the water collecting well to lower the water level. Depressurize the water box to depressurize the horizontal drain material, make the water collection well a closed structure, depressurize the water collection well with drainage to depressurize the water shield box, and use the horizontal drain material as the water shield box. It is preferable to fix it in advance on the top of the body and to install it at the same time as the impermeable box is installed on the surface of the water bottom ground.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

In the drawings, reference numeral 1 indicates a water shield box 1 used in the method of the present invention. This water-blocking box 1 has a vertically oriented cylindrical water-permeable wall 1a that penetrates into the soil and has a top plate 1 at the top.
It is formed in a lower end open type closed by b. A water absorbing hole is formed in the top plate 1b of the water shield box 1, and a decompression hose is connected to the water absorbing hole.

In carrying out the method of the present invention, first, the drain material placing sections 10, 10 ... With the size of the above-mentioned impermeable box 1 as one unit are set side by side on the water bottom ground to be constructed. As shown in FIG. 3, the drain material driving sections 10 are set to have a predetermined space a between the adjacent sections 10 and 10. The interval a is a predetermined (later described) interval wider than the drain material placement interval b in each section 10.

Next, as shown in FIG. 4, a large number of vertical drain members 12, 12, ... Are placed in each section 10 at regular intervals b using a drain member placing ship 11 floating on the water surface. . As shown in the figure, the vertical drain member 12 is driven with its upper end protruding from the water bottom by a predetermined length.

The drain material placing interval b is determined in consideration of the drainage efficiency of the soil pore water in the ground and the economical efficiency of the drain material used, depending on the softness of the water bottom ground and the fluidity of water in the ground.

As the drain material to be used, a plastic board drain material, a fiber drain material using natural fibers, a drain material consisting of a perforated pipe, a drain material consisting of a sand column, a water-permeable woven cloth bag filled with sand or crushed stone. A bag material, a drain material in which non-woven fabrics are overlapped to give water permeability, or the like can be used, but a plastic board drain material is preferable.

In this way, the vertical drain members 12, 12
.. is placed in each section 10, 10 ..
For each 0, a horizontal drain 13 made of sand mat is laid by embedding the upper end of the vertical drain member 12.

Next, as shown in FIG. 5, the above-mentioned water shield box 1 is put on the horizontal drain 13 for each of the drain material placement sections 10, 10. When installing the water shield box 1, the crane ship 14 is used and the water shield box 1 is installed.
By fixing the frame-shaped mounting jig 15 on the top, suspending this with the hanging wire 16a of the crane 16 and lowering it to the water bottom, depending on the weight of the water shield box 1 and the mounting jig 15,
Penetration of soil The impermeable wall 1a is penetrated into the ground. In this way, the water shield box 1 is covered so that the horizontal drain 13 is housed inside the top part thereof.

In this way, each drain material placement section 10
The water-blocking box 1 is covered and the mounting jig 15 is removed, and the decompression hose 17 is connected to each water-blocking box 1 water-absorbing hole as shown in FIG. 6, and this is connected to the bottom of the water collecting well 18.

The water collecting well 18 is composed of an airtight tank, a submersible pump 19 for drainage is accommodated in the bottom portion thereof, the water in the water collecting well 18 is discharged through a drainage pipe 20, and a vacuum pump 21 is provided at the top portion. The decompression pipe 22 is connected, and this decompression pump enables decompression of the water collection well 18.

In this way, the decompression hoses 17 of the plurality of water shield boxes 1 and 1 adjacent to each other are connected to the water collecting well 18 to discharge the water in the water collecting well 18 to lower the internal water level and to vacuum the vacuum pump. The inside is decompressed by 21. As a result, the pressure difference between the pressure in the water collecting well 18 and the atmospheric pressure is applied to the top surface of the water-blocking box 1, and the consolidation and dehydration are promoted.

In addition, although not shown in the figure, the collection well 18 may be a vertically long tank having an open upper end. In this case, the collection well 18 has a length from the bottom to the surface of the water. The water level in the tank is lowered by discharging the water in the water collecting well 18 through the drain pipe 20 by the submersible pump 19 for drainage which is formed and stored in the bottom. As a result, when the water level in the water collection well 18 becomes lower than the outer water level, the pressure in the impervious box 1 is reduced by the pressure difference caused by the head difference h, and this causes the vertical drain member 12 to pass through the vertical drain material 12 to remove the soft ground. Dehydration and consolidation by water pressure are performed.

By depressurizing the inside of the water-blocking box 1 in this manner, the drainage of the soft ground of each drain material placing section 10, that is, the soft ground A below the water-blocking box, can be consolidated. As shown in FIG. 8, the soft ground A is compacted in the vertical direction and also contracts in the horizontal direction at the same time. Due to this contraction, the soft ground between the adjacent water-blocking boxes 1 and 1, the immediate water-blocking box. The soft ground B is drawn in and the surface of the ground is lowered.

The degree of deterioration of the soft ground B between the water-blocking boxes, that is, the degree of decrease of the soft ground B between the water-blocking boxes with respect to the subsidence of the surface of the soft ground A below the water-blocking box is calculated in advance by soil investigation. In advance, the construction is carried out by selecting the drain material driving sections 10, 10 in advance, that is, the interval a between the water blocking boxes 1, 1 so that the subsidence amounts of both grounds A, B are the same. As a result, it is possible to simultaneously reduce the relatively wide water-blocking inter-body soft ground B on which the vertical drain material 12 is not placed.

In the above example, a sand mat is used for the horizontal drain 13, but as shown in FIG.
A horizontal drain member 13a made of a water-permeable material such as a non-woven fabric is housed in the top of the water shield box 1, and the vertical drain member 12
After placing, by covering the impervious box 1 on it,
It may be configured by a horizontal drain 13a communicating with the vertical drain member 12.

Test example In the present invention 1. Understanding of subsidence deformation behavior of soft ground and impermeable box 1 2. Improvement effects such as sinkage and volume reduction 3. Grasp the settlement behavior when multiple water shield boxes 1 are installed The indoor model experiment was conducted for the purpose.

Soil to be tested Soil type marine clay shown in Table 1.

Experimental apparatus 1. Single experiment soil tank 23: length 150 cm x width 150 cm x depth 10
0 Water-blocking box 1: Polycarbonate box, length 30 cm x width 30 cm x penetration depth in the soil Impermeable wall 2
0cm Horizontal drain material 13: Non-woven fabric Vertical drain material 12: Non-woven fabric As shown in Fig. 10 and Fig. 11, the soil to be tested is accommodated in the soil tank 23, and one drain material placing section is set in the center of the soil. Vertical drain material 12, horizontal drain 1
Three materials and a water shield box 1 were installed. 2. Soil 23 for multiple experiments: length 150 cm x width 150 cm x depth 10
0 Impermeable box 1: Polycarbonate box, length 25 cm x width 25 cm x penetration depth of soil
0 cm Horizontal drain 13 materials: Non-woven fabric Vertical drain material 12: Non-woven fabric As shown in Fig. 12 and Fig. 13, put a partition plate 24 in the other soil tank 23 and set it on one side to set 9 drain material placement sections. As shown in the drawing, the vertical drain member 12, the horizontal drain member 13 and the water shield box 1 were installed.

Experimental Results As a result of decompressing the inside of the water shield box 1 in each test device, the result shown in FIG. 14 was obtained in the single test device, and the experimental result shown in FIG. 15 was obtained in the plural test device.

According to this, when a single impermeable enclosure 1 is used, the effect of subsidence extends to the surrounding ground as shown in FIG. 14 and extends to a point 60 cm away from the impermeable enclosure 1. It became a result.

On the other hand, when a plurality of water-blocking boxes 1 are used side by side, the ground between the water-blocking boxes 1 is 5 to 10 cm compared to the top of the water-blocking box 1 at the end of the experiment as shown in FIG.
The phenomenon of sinking also occurred. This phenomenon was because, as shown in FIG. 16, the clay between the water-blocking boxes 1 and 1 dropped (sinks) toward the vertical drain material 12 while being consolidated.

From the above results, the spacing and the subsidence shape between the water-blocking boxes 1 are as shown in FIG. 17A when the spacing is too small and when the spacing is too wide. 17
As shown in (b), the subsidence between the boxes became insufficient, and it was found that the boxes were settled uniformly between the boxes as shown in FIG. 17 (c) by appropriately setting the interval.

[0033]

As described above, the method for reducing the volume of soft-bed soft ground according to the present invention has a vertically open cylindrical water-impervious impermeable wall, and the open bottom end with the top end closed. Using the water-blocking box of the above, on the surface of the soft ground of the bottom of the water, the drain material casting section in the unit of the size according to the size of the water-blocking box,
A plurality of vertical drain materials are set at intervals wider than the vertical drain material intervals in the drain material driving section, and a large number of vertical drain materials are driven from the water bottom soft ground surface for each of the drain material driving sections and the water bottom A horizontal drain material that is continuous with each vertical drain material is installed on the soft ground surface, and the impermeable box body is arranged to cover the upper surface of the soft drain surface, and the soil penetrating impermeable wall is penetrated into the soft ground to cover it. After that, by simultaneously decompressing the horizontal drain material inside each of the impermeable boxes installed next to each other, it was possible to dehydrate the water bottom soft ground to reduce the volume, thus consolidating the conventional soft ground. Compared with the volume reduction method, it is possible to make a wider area where the vertical drain material is not placed between the water shield boxes, and it is possible to reduce the number of vertical drain materials used, which reduces the cost of materials used and the vertical drain materials. Hitting Work is also reduced, to reduce the construction cost,
The construction period can be shortened and the economy is high.

Further, the ground between the water-blocking boxes is submerged in accordance with the interval between the water-blocking boxes between the adjacent drain material casting sections to the subsidence of the water-bed soft ground surface caused by the dehydration of each section. By setting the length, the water bottom ground after volume reduction can be made flat.

Further, the water collecting well installed on the bottom of the water and the water blocking body are communicated with each other through a drain pipe, and the water inside the water collecting well is drained to reduce the water level, thereby depressurizing the water blocking body. By depressurizing the inside of the horizontal drain material,
It is possible to decompress the inside of the impermeable box only by drainage, and it is possible to consolidate drainage without requiring a large decompression pump.

Further, the pressure reduction efficiency can be improved by making the water collection well have a closed structure and reducing the pressure inside the water collection well together with the drainage.

Further, the horizontal drain material is fixed in advance on the top of the water-blocking box, and is installed at the same time when the water-blocking box is installed on the surface of the water bottom ground, so that the horizontal drain material can be installed on the bottom of the water. It is carried out at the same time as the installation of the water-blocking box, and can be easily reused after construction, which is highly economical.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an example of a water-blocking box used in the present invention.

FIG. 2 is a plan view of the above.

FIG. 3 is a plan view showing drain material section setting in an example of implementation of the method of the present invention.

FIG. 4 is a vertical cross-sectional view showing a vertical drain material placing step of the above.

FIG. 5 is a vertical cross-sectional view showing the step of installing the water-blocking box after the installation of the horizontal drain using the above sand mat.

FIG. 6 is a vertical sectional view showing a consolidation dehydration step of the above.

FIG. 7 is a vertical cross-sectional view showing a state in which the volume has been reduced by consolidation dehydration as above.

FIG. 8 is a sectional view showing the consolidation principle of the above.

FIG. 9 is a vertical cross-sectional view showing a water shield box installation step in another embodiment of the method of the present invention.

FIG. 10 is a plan view showing experimental equipment using a singular box of the present invention.

FIG. 11 is a vertical sectional view of the above.

FIG. 12 is a plan view showing an experimental facility using a plurality of boxes according to the present invention.

FIG. 13 is a vertical sectional view of the above.

FIG. 14 is a graph showing an experimental result when a singular box is used.

FIG. 15 is a graph showing an experimental result when a plurality of boxes is used.

FIG. 16 is a vertical cross-sectional view showing the principle of subsidence between water-blocking boxes according to experimental results.

FIG. 17 is a cross-sectional view showing the relationship between the water-blocking box spacing and inter-box ground subsidence based on experimental results.

[Explanation of symbols]

A soft ground below the water-blocking box B Soft impermeable box Ground a, b interval 1 Impermeable box 1a Underground seepage barrier 1b Top plate 10 Drain material placement section 11 Drain material placing ship 12 Vertical drain material 13 Horizontal drain 13a Horizontal drain material 14 crane ships 15 Mounting jig 16 cranes 16a hanging wire 17 Decompression hose 18 collecting wells 19 Submersible pump 20 drainage pipe 21 vacuum pump 22 Decompression pipe 23 earthen tank 24 partition boards

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinsha Hiroshi             Tochigi Prefecture Nasu-gun Nishinasuno-cho 4 Ward-cho 1534-1             Goyo Construction Co., Ltd. Technical Research Center F-term (reference) 2D043 CA04 DA09 EB05

Claims (5)

[Claims] 1. A vertically oriented tubular impermeable water barrier in the periphery,
An open water shield box with a closed top is used, and a drain material placing section is set on the surface of the water-bed soft ground in units of the size corresponding to the size of the water shield box. A plurality of vertical drain materials are set at intervals wider than the vertical drain material spacing in the drain material driving section, and a large number of vertical drain materials are driven from the surface of the water bottom soft ground for each of the drain material driving sections. A horizontal drain material that is continuous with each vertical drain material is installed on the surface of the water-bottom soft ground, and the impermeable box body is arranged to cover the upper surface of the water, and the soil penetrating impermeable wall is penetrated into the soft ground to cover it. After that, by simultaneously decompressing the horizontal drain material inside each of the impermeable boxes installed next to each other, the volume of the water-bed soft ground is reduced by dehydrating the water-bed soft ground to reduce the volume. Chemical method. 2. The ground between the water-blocking boxes is submerged in accordance with the distance between the water-blocking boxes between the adjacent draining material casting sections to the subsidence of the water-bottom soft ground surface caused by the dehydration of each section. The volume reduction method for soft-bed soft ground according to claim 1, wherein the volume is set to a length. 3. A water collecting well installed on the bottom of the water is communicated with a water blocking body through a drain pipe, and the water inside the water collecting well is drained to lower the water level to reduce the pressure inside the water blocking housing. 3. The method for reducing the volume of water-bed soft ground according to claim 1, wherein the inside of the horizontal drain material is decompressed. 4. The volume-reducing method for soft-bed soil according to claim 3, wherein the water collecting well has a closed structure, and the water inside the water collecting well is decompressed together with drainage. 5. The weak water bottom according to claim 1, wherein the horizontal drain member is fixed in advance on the top of the water shield box and is installed at the same time when the water shield box is installed on the surface of the water bottom ground. Ground volume reduction method.