JPH0711868A - Fluidizing method of shield excavated soil - Google Patents

Abstract

PURPOSE:To reduce the cost of the preparation and impregnation of additives by ensuring the fluidity of excavated soil without using additives at all. CONSTITUTION:High pressure water is injected into a chamber 2 through a turbine pump 6 from a water tank 5 in the chamber 2 of a shielding machine 1. Effective stress (p) working among soil particles (a) in the chamber 2 taken in with the excavation of the shielding machine 1 is reduced, the frictional resistance of gravelly soil is lowered, and agitation by an agitating blade 4 is facilitated, thus ensuring the fluidity of shield excavated soil in the chamber 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 fluidizing the excavated soil taken into the chamber as the shield machine is dug when the earth pressure type shield construction method is applied to the gravel ground.

[0002]

2. Description of the Related Art Sandy soil and gravel soil have a large internal friction angle,
It is difficult to secure the fluidity because the soil has a large frictional resistance, and when the excavated soil is filled in the chamber of the shield machine, the cutter torque increases, which makes steady excavation difficult. Further, when the blockage phenomenon due to the excavated soil occurs in the chamber, it becomes difficult to propel the shield machine itself. For this reason, for such ground, the face face,
Alternatively, a method of injecting various additives into the chamber and forcibly stirring with a stirring blade to secure the fluidity of the excavated soil in the chamber is used.

As additive materials, bentonite, mud making materials using clay, and shaving cream-like bubbles made from special foaming agents are used.

[0004]

In the above-mentioned conventional method, when an additive is used, the apparatus itself for producing and injecting the additive becomes large in scale, and the material cost increases depending on the kind of the additive. Furthermore, when bentonite or clay is used, the amount of soil generated by excavation is large, and moreover, it becomes sludge-like, so that there is a problem that a large amount of cost is required for the treatment of residual soil.

The present invention has been proposed in view of the above-mentioned problems of the prior art. The object of the present invention is to secure the fluidity of excavated soil without using any additive material as in the prior art. The purpose is to provide a fluidization method for shield excavated soil, which can reduce the cost of producing and injecting additive material and the cost of processing residual soil of generated soil.

[0006]

To achieve the above object, according to the method for fluidizing shield excavated soil according to the present invention, high-pressure water higher than groundwater pressure is injected into the chamber of the shield machine. The effective stress acting between the soil particles taken into the chamber with the propulsion of the shield machine is reduced to reduce the frictional resistance of the gravel soil.

[0007]

When the excavated soil taken into the chamber of the shield machine is stirred, the shearing force of the soil resists the stirring blade. At this time, when the earth and sand taken into the chamber is gravelly soil, the frictional resistance between the soil particles and the meshing of the soil particles are the main components of the shear resistance of the soil. Due to the principle of effective stress of the soil, these strength components are proportional to the effective stress, so that the shear of the gravel soil taken into the chamber may be reduced.

According to the present invention, as described above, by injecting water having a pressure higher than the groundwater pressure into the chamber, when the excess pore water pressure is generated between the soil particles, the effective stress of the soil is reduced. Further, since the inside of the chamber is temporarily in an undrained shearing state, the shearing force of the soil resisting the agitating blades is sharply reduced and the soil becomes fluid.

[0009]

The present invention will be described below with reference to the illustrated embodiments. 1 is a shield machine, 2 is a chamber, 3 is a cutter face plate, and 4 is a stirring blade. A water tank 5 is disposed behind the chamber 2 in the shield machine 1, and water having a pressure higher than groundwater pressure is injected into the chamber 2 from the water tank 5 via a turbine pump 6. Since the turbine pump 6 has a structure that prevents backflow of groundwater into the water tank 5, it becomes possible to inject it into the chamber 2 at a pressure higher than that pressure when the groundwater pressure is high.

The high-pressure water thus injected into the chamber 2 raises the groundwater pressure in the chamber to generate excess pore water pressure. At this time, as shown in FIG. 3, the effective stress p between the soil particles a is reduced, the shearing resistance of the soil is reduced, the excavated soil in the chamber 2 is easily stirred by the stirring blade 4, and the excavated soil is fluidized. Let The excess pore water pressure generated in the chamber 2 also increases the pore water pressure q of the ground on the front surface of the cutter face plate 3, reduces the frictional force between the ground and the cutter face plate 3, reduces the cutter torque, and reduces the shield machine 1 It has the additional effect of increasing the digging speed of.

It should be noted that the injection position of the high-pressure water must be positioned above the intake port 7 in order to prevent reverse flow of water pressure to the screw conveyor. Further, in a shield machine with a large cross section, in order to make the water pressure in the chamber 2 uniform, it is desirable to inject above the intake port 7. Further, the water to be injected into the chamber 2 is supplied from the outside of the shield machine 1 or when the soil is discharged from the screw conveyor, only water is separated,
It is also possible to store it in the water tank 5 and inject it.

In the figure, 8 is a screen and 9 is a cutter bit.

[0013]

According to the present invention, as described above, the excavated soil taken into the chamber of the shield machine by injecting water having a higher water pressure than the groundwater pressure water into the chamber of the shield machine. By generating the pore water pressure of the soil particles and reducing the effective stress acting between the soil particles,
Since it is possible to fluidize the excavated soil simply by changing the pressure state of the groundwater, the soil generated by the shield machine remains in the soil condition of the ground, and the generated soil cannot be disposed or reused. It will be easy. In addition, making additive materials,
The injection becomes unnecessary and the cost required for this can be saved.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an implementation state of an embodiment of a method for fluidizing shield excavated soil according to the present invention.

FIG. 2 is an explanatory diagram of a method for fluidizing excavated soil in a chamber of a shield machine.

FIG. 3 is a conceptual diagram of effective stress of soil particles and pore water pressure.

[Explanation of symbols]

 1 Shield Machine 2 Chamber 3 Cutter Face Plate 4 Stirring Blade 5 Water Tank 6 Turbine Pump 7 Inlet 8 Screen 9 Cutter Bit

Claims (1)

[Claims] 1. A high pressure water higher than groundwater pressure is injected into a chamber of a shield machine to reduce effective stress acting between soil particles taken into the chamber as the shield machine is propelled to reduce gravel and gravel. A fluidization method for shield excavated soil, which is characterized by reducing frictional resistance of soil.