JPH05280034A - Method of improving ultra weak foundation - Google Patents

Abstract

(57) [Summary] [Purpose] Efficiently improve ground from the surface of ultra-soft ground due to pump dredging sludge by vertical drain. [Structure] A work boat 3 is floated on an ultra-soft ground 2, a hollow cylindrical drain 4 is driven from the work boat 3 to a point before a basin of a predetermined depth, and then the upper end of the drain 4 is cut into a predetermined length.
The drain hose 8 is connected to the upper end. After that, the drain 4 is driven to a predetermined depth where the upper end is lower than the ground surface, and the drain hose 8 is connected to the negative pressure pipe 9. After the driving of the drain 4 is completed, the surface of the ground 2 is covered with the sealing sheet 11, the pressure in the negative pressure pipe 9 is reduced, and the negative pressure is applied to the ground 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving ultra-soft ground for draining ultra-soft ground caused by dredging sludge at the time of dredging sludge by a pump type dredger.

[0002]

2. Description of the Related Art Generally, when dredging sludge is stored in a processing facility, it becomes extremely soft ground having extremely high fluidity. Conventionally, the following methods have been used to improve such ultra-soft ground. (1) Since embankment cannot be directly formed on the ground surface, the surface layer of ultra-soft ground is first solidified with a hardening agent, or geotextile is laid to reinforce the bearing capacity, and soil is covered on it. This soil cover will secure the troughability for loading the ground improvement machine. Next, a method of carrying in a drain driving machine and placing a vertical drain from above the soil cover to cover the loaded soil. (2) A work vessel for horizontal drain installation is floated on the water surface of ultra-soft ground, and the horizontal horizontal drain is laid in multiple stages by moving horizontally from the drain guide projecting below the bottom of the ship while extending the drain. Then, a negative pressure is applied to the ground from the horizontal drain to drain the water. (3) A method in which a drainage pipe and a vertical drain are installed in advance in the dredging sludge treatment facility, the dredging sludge is put into the treatment facility from a pump ship, and a negative pressure is applied to the ground through the vertical drain to drain the water.

[0003]

Among the above-mentioned methods,
In the case of the method of securing the trafficability by covering the soil in (1), two types of improvement processes are required: surface solidification, surface treatment such as soil covering, and ground improvement after covering the soil. Especially in the case of ultra-soft ground, the trafficability is improved. There is a problem that it takes a lot of money and a long time to secure the above.

In the horizontal drain laying method of (2), since the drain laying depth in one drain laying work is relatively shallow, the horizontal drain laying work must be performed every time the dredging sludge is fed to a constant thickness. However, the dredging work is divided in time, which causes a problem in work efficiency.

Further, in the method (3) in which a drainage facility and a vertical drain connected to the drainage facility are installed in advance in the treatment facility, when the treatment facility is under the sea, it becomes an underwater operation, and the drainage facility, etc. There is a problem that the installation work is difficult and it is difficult to install the vertical drain straight in the ground at regular intervals.

The present invention has been made for the purpose of providing a method for simultaneously solving all the various problems of such work.

[0007]

The feature of the method for improving ultra-soft ground of the present invention to solve the above-mentioned conventional problems is that a hollow cylindrical drain is provided from a work boat floating on the ultra-soft ground. After driving to a depth just before the driving depth, cut the upper end of the drain to the planned driving length, connect one end of the drainage hose to the upper end, and then, after the upper end of the drain is Repeating the step of driving to a predetermined depth below the surface of the soft ground to drive a large number of drains at regular intervals in the vertical direction, and then applying a negative pressure to the ground through the drain hose and drain material. is there. Further, after the drain is driven vertically, the ground surface may be covered with a sealing sheet.

[0008]

In the method of the present invention, after the drain is driven to a depth before the drainage of the drain material at a predetermined depth, the upper end is cut into a predetermined length. This predetermined length is such that the upper end is a depth below the surface of the ground, preferably about 0.5 m, when the drain is completely driven. Therefore, when the final driving is completed, the lower end of the drain reaches the bottom of the ultra-soft ground and the upper end of the drain is positioned about 0.5 m below the surface of the ground.

In this way, the drain hose is connected to, for example, a negative pressure pipe to reduce the pressure in a state where a large number of drains are driven in accordance with the depth of the ultra-soft ground. Is operated and drained through the drain and drain hose.

[0010]

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

FIG. 4 shows equipment for carrying out the present invention. In the figure, reference numeral 1 is an embankment which constitutes a dredging treatment facility, and 2 is an ultra-soft material retained in a mud storage area surrounded by the embankment. It is the ground. During this ultra-soft ground improvement, the work boat 3 is floated on the surface thereof. The work boat 3 is provided with a mandrel 6 in which a hollow cylindrical plastic board drain 4 is wound around a reel 5 and is driven along the longitudinal direction. A drain 4 is driven from above the work boat 3 at regular intervals. When driving the drain 4, as shown in FIG. 1 (a), before the lower end reaches the bottom of the ultra-soft ground, the upper end is cut to a required length on the work boat 3 and the hose connecting cap 7 is attached to the upper end. The drain hose 8 is connected by fitting. The cutting length of the drain 4 is such that the lower end reaches the bottom of the ultra-soft ground 2 and the upper end is the ultra-soft ground 2.
Cut into a predetermined length according to the depth of each driving part so that the length is located about 0.5 m below the surface. After connecting the drainage hose 8 on the work boat 3 in this way, the mandrel 6 is further penetrated and the drain 4 is driven to a predetermined depth as shown in FIG.
Lift the mandrel 6 while leaving it inside. After that, the other end of the drain hose 8 is connected to the negative pressure pipe 9. This negative pressure piping 9
Is floated on the water surface of the ground 2 in advance for each row of driving the drains 4, and a joint 10 (FIG. 3) for connecting the drainage hoses of each drain or collectively the drainage hoses of a plurality of drains is used. (Shown in FIG. 4) is used in advance.

In this way, the drains 4, 4, ... Are laid, and the drain hose 8 and the negative pressure pipe 9 are connected.
As shown in (c), the sealing sheet 1 is provided on the surface of the ground 2.
Laying 1 Next, each negative pressure pipe 9 is decompressed by the decompression pump 12. As a result, a negative pressure is applied to the ground 2 through the drain hose 8 and the drain 4, and moisture in the soil is sucked out through the drain 4 and is consolidated.

Although the sealing sheet 11 is used in the above embodiment, it is not always necessary in some cases.

[0014]

As described above, in the method for improving ultra-soft ground of the present invention, a vertical drain is installed by driving a drain from the surface of the ground, and a negative pressure is applied to the ground through the drain to consolidate the ground. Therefore, it is not necessary to perform the treatment for producing the ground trough traceability before the improvement, and even the deep ultra-soft ground can be worked from the surface according to the depth, Effects such as inserting a certain amount of sludge as in the case of installing a horizontal or vertical drain in the ground, eliminating the need for work for each thickness and underwater work, and making it easy to evenly install the drains at predetermined intervals. There is.

Further, since the upper end of the drain is driven completely below the surface of the ground, air is not sucked in when a negative pressure is applied, and drainage in the ground is efficiently performed. Further, this action is more effectively performed by covering the ground surface with a sealing sheet.

[Brief description of drawings]

1A to 1C are sectional views showing working steps of a method of the present invention.

FIG. 2 is a plan view of a state after the drain is cast by the method of the present invention.

FIG. 3 is a perspective view showing a connected state of the drain, the drain hose, and the negative pressure pipe of the above.

FIG. 4 is a cross-sectional view showing ground improvement equipment.

[Explanation of symbols]

 1 Embankment 2 Ultra-soft ground 3 Work boat 4 Plastic board drain 5 Reel 6 Mandrel 7 Hose connecting cap 8 Drain hose 9 Negative pressure piping 10 Joint 11 Sealing sheet

Claims (2)

[Claims] 1. A hollow cylindrical drain is driven from a work boat floating on an ultra-soft ground to a depth before the basin of a predetermined driving depth, and then the upper end of the drain is cut into a predetermined driving length, Connect one end of the drainage hose to its upper end, and then repeat the process of driving the drain until its upper end reaches a predetermined depth below the surface of the ultra-soft ground, and vertically arrange a number of drains at regular intervals. A method for improving ultra-soft ground, characterized by applying a negative pressure to the ground through the drainage hose and the drain material after placing. 2. A hollow cylindrical drain is driven from a work boat floating on an ultra-soft ground to a depth before the basin of a predetermined driving depth, and then the upper end of the drain is cut into a predetermined driving length, Connect one end of the drainage hose to its upper end, and then repeat the process of driving the drain until its upper end reaches a predetermined depth below the surface of the ultra-soft ground, and vertically arrange a number of drains at regular intervals. A method for improving ultra-soft ground, which comprises casting, covering the surface of the ultra-soft ground with a sealing sheet, and then applying a negative pressure to the ground through the drainage hose and drain material.