JPS62280419A - Dumping of soil onto soft bottom ground under water - Google Patents

Abstract

PURPOSE:To enhance the dumping yield of soil by preventing the penetration of soil into the ground by impact pressures by a method in which a highly rigid flat plate is set on soft bottom ground under water, soil is dumped onto the plate, and the flat plate is pulled up. CONSTITUTION:A highly rigid flat plate 3 is set on the soft bottom ground 1 under water through a rope 4, and soil is dumped from a soil barge 2 onto the plate 3. The flat plate 3 is inclined and pulled up by the rope 4. The dumping operation of soil can thus be economically made without the penetration of soil into the ground 1.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Technical Field of the Invention] The present invention is aimed at preventing the digging of earth and sand due to the impact pressure applied to the soft ground when earth and sand is lifted from an earth carrier onto soft ground such as the seabed. This relates to a preventable method of dropping earth and sand onto soft ground at the bottom of the water.

[Prior art]

In view of the early use of reclaimed land and environmental regulations, relatively good quality sandy soil is used as reclamation material in recent reclamation works.

However, except for some areas, Japan's coastal areas are made up of soft seabed clay, making it difficult to obtain high-quality reclamation materials. For example, 5. 7 from OO0Ton,
0OOT.

A method has been used in which soil is loaded onto a large purge vessel with n-load capacity, and then a large amount of soil is dropped directly onto the soft ground on the seabed at a landfill site.

However, in this construction method using earth carriers, large amounts of earth and sand are dropped instantaneously, and the impact energy generated when the dropped earth and sand collides with the seabed causes the seabed to be made up of soft ground. It is known that in some places, dumped earth and sand can penetrate up to 1 to 2 meters into the soft ground.

Therefore, if the thickness of the reclaimed layer is considerably thicker than the above-mentioned sinking, there is no problem, but in cases where the thickness of the sand layer is from several centimeters to 2 meters at most, such as sand mats for ground improvement or sand covering for artificial beaches. In this case, it has been difficult to determine the yield rate because the penetration depth of 1 m to 2 m accounts for an extremely large proportion of the required sand layer thickness.

Conventional construction methods that attempt to minimize the amount of denting mentioned above include a method using a gas vessel, a method using a tremie tube, and a method using a purge unloader.

However, all of these methods focus on reducing the impact pressure when dropping sand by scattering a small amount of sand on soft ground, so these methods require a long time to complete. However, even if these methods are used, it is impossible to completely prevent sinking, and the work cost is high.

Therefore, as shown in FIG. 8, the present inventors have developed a mechanism for destroying the soft ground 1 and a mechanism for depositing the spread soil when soil is laid over the soft ground 1 on the seabed from the bottom of the earth transport vessel 2. As a result of conducting an experiment focusing on this, it was found that the earth and sand laid down by the earth carrier 2 forms a lump of earth A shown by a broken line and collides with the soft ground 1 on the seabed, and the seabed ground 1 is destroyed by this impact pressure. It was found that the dumped soil sinks into soft ground 1 as shown by arrow B.

The above-mentioned thrown earth and sand B has much higher rigidity than the soft ground 1, and when earth and sand is thrown on top of it again, it collides with the surface of this thrown earth and sand B as shown in Figure 9.
It was confirmed that the soil C that was dropped for the second time caused a large spread as it slid on the surface of the sand layer, and that the sinking caused by the spread soil was almost negligible, as shown in Figure 9.

[Purpose of the invention]

As mentioned above, the present invention was made by paying attention to the characteristics of the earth and sand placed over soft ground from an earth transport ship. The purpose is to prevent the ground from sinking into soft ground.

[Structure of the invention]

In order to achieve the above object, the method of dropping earth and sand onto the soft ground on the water bottom of the present invention is such that a flat plate body having higher rigidity than the soft ground is placed in advance on the soft ground on the water bottom where earth and sand is to be dropped from an earth carrier. The method is characterized in that the flat plate body is pulled up after dropping earth and sand onto it.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of dropping earth and sand onto soft ground at the bottom of a water body using the earth and sand dropping method of the present invention will be described below with reference to the drawings.

First, in Example 1 shown in FIG. 1 and subsequent figures, a continuous flat plate body 3, which is much more rigid than the soft ground 1 on which the earth and sand S is to be dropped onto the bottom of the earth transport vessel 2, such as a purge ship, transporting earth and sand S, For example, an iron plate is installed via a wire 4 (or chain), a winch 5, and the like.

The size of the flat plate 3 may be slightly larger than the width and length of the direct purge outlet 6, for example, about 110 m x 75 m.

Therefore, when the soil transport ship 2 arrives at the soil dropping point, the second
As shown in the figure, the flat plate body 3 is lowered by a wire 4 and previously landed on the soft ground 1 of the seabed onto which earth and sand S is to be dropped.

The ground pressure P of this flat plate body 3 is, for example, when using an iron plate with a thickness of 1 cm, the specific gravity of iron is 7.9, and the buoyancy is 1.
If it is set to 0, it is as follows.

P=(7,9-1,0) Xl, Og/co! =6.9
g/cal Hakama 0.007Kg/cffl Also, the strength C of the soft ground 1 required to support the above ground pressure P is q
= 5.5 C, C=0.0014kg/c
al = 0.014 t/rri.

For example, according to data surveyed in the Tokyo Bay area, it has been reported that the strength of the sludge surface layer of soft ground 1 with a moisture content of 300% to 450% is C-0, Q5t/nf, and the ground pressure P (0 , 07t/rrf).

Next, the earth and sand S is dropped onto the flat plate body 3 from the barge direct dumping port 6 of the earth transport vessel 2 as shown in FIG.

The dropped soil S collides with the flat plate 3, which has extremely high rigidity, and generates a large lateral flow as shown by the arrow H, which spreads over a wide area as shown in Fig. 4. This greatly reduces the amount of soil S that sinks into the soft ground 1. can be reduced to

After the earth and sand S has been dropped, the wire 4 or chain attached to the flat plate 3 is wound up with a winch 5 and set on the bottom of the earth transport vessel 2, as shown in FIG.

Next, the front sectional view of FIG. 6 and the side view of FIG. 7 show a second embodiment of the present invention. The flat plate 3 is bent in two at the center, and after dropping the earth and sand S, by pulling up the wire 4 attached to the center of the flat plate 3, the upper sand S on the flat plate 3 is removed from the left and right sides of the flat plate 3. It is designed to be laid separately on soft ground 1.

In addition, in the above-mentioned Examples 1 and 2, an example is shown in which the flat plate body 3 is hung and installed at the bottom of the soil transport vessel 2 itself that drops the earth and sand S, but regarding the installation position of this flat plate body 3, etc. is not particularly limited to these embodiments 1.2, and for example, the flat plate body 3 loaded on the earth transport vessel 2 or on another purge etc. may be placed on the soft ground 1 where the earth and sand S is to be dropped as appropriate. The earth and sand S may be dropped onto the bottom by moving the earth transport vessel 2 onto the bottom.

〔Effect of the invention〕

As explained above, if the method of the present invention is adopted, the impact pressure applied to the soft ground by the earth and sand carried by the earth transport vessel will be absorbed by the flat plate, and the impact pressure will be applied to the soft ground. It prevents sinking, and enables soil to be laid on soft ground with an even thickness and with high efficiency, improving the soil yield rate and significantly reducing the amount of soil used, making it possible to perform economical soil dumping operations. effective.

The sand dropping method of the present invention can be used for high-yield and rapid construction of sand mats on soft underwater ground, for creating artificial beaches by covering underwater sludge, and for preventing contamination by covering sludge with sand. It can be effectively used as a measure to increase fishery resources by covering sludge with sand.

[Brief explanation of the drawing]

Figures 1, 2, 3, 4 and 5 are schematic normal cross sections showing the procedure in Example 1 when dropping earth and sand onto soft ground at the bottom of water using the earth and sand dropping method of the present invention. Fig. 6 is a schematic front sectional view of Example 2 of the present invention, Fig. 7 is a side view of Fig. 6, and Figs. 8 and 9 are schematic explanatory views showing experimental results in the conventional earth and sand dropping method. It is. 1...Soft ground, 2...Earth transport ship, 3...Slab body,
4...wire, S...earth and sand.

Claims (1)

[Claims] A method of softening the water bottom by placing a flat plate that is more rigid than the soft ground in advance on the soft ground of the water bottom onto which earth and sand is dropped from an earth transport ship, and then pulling up the flat plate after dropping the earth and sand on top of the soft ground. Method of dropping earth and sand into the ground.