JP6401574B2 - Pneumatic caisson method - Google Patents

Description

  The present invention relates to a pneumatic caisson method, and more particularly to a pneumatic caisson method capable of efficiently supplying air into a work chamber.

  In the pneumatic caisson method, a caisson work room is provided at the bottom of the housing, and compressed air equivalent to groundwater pressure is sent into the caisson work room to suppress the inflow of groundwater into the caisson work room, and excavation is performed in the caisson work room. This is a construction method that builds an underground structure by sinking the skeleton into the ground while performing. The underground structures constructed by the pneumatic caisson method include bridges and foundations of structures, underground adjustment ponds, shafts of shield tunnels, and subway and tunnel main structures.

  Specifically, a blade that has an acute angle downward is provided at the lower end of the caisson working chamber provided at the bottom of the cylindrical casing, and the cylindrical casing is formed by its own weight and loading. Sunk into the ground. Thereafter, the cylindrical casing is added and used as a load when the cylindrical casing is sunk while making the cylindrical casing a desired size (see, for example, Patent Document 1).

JP2013-87550A

  As described above, in the pneumatic caisson method, it is necessary to set the air supply pressure so that the amount of groundwater flowing into the caisson work chamber becomes an appropriate amount, and to manage the air pressure pumped into the caisson work chamber. However, the current situation is that the air supply pressure for the appropriate amount of groundwater inflow cannot be determined uniformly depending on the soil quality, hydraulic conductivity, etc. of the construction site.

That is, it is necessary to plan and construct the working air pressure so that the amount of groundwater flowing from the bottom of the caisson work room becomes the amount of water allowed for work. This working air pressure is determined based on the depth from the average underground water surface to the blade edge and the coefficient corresponding to the soil quality and the like. The working pressure is obtained by the following equation (1).
P _w = 0.0098 × m (H + 1.0) Formula (1)
However,
P _w : Working atmospheric pressure (MPa)
H: Depth (meter) from average water surface to blade edge
m: Coefficient corresponding to soil quality

  According to the Japan Pressure Technology Association guidelines, the coefficient m is determined as shown in Table 1 below. However, in actual construction, the working air pressure determined in this way may not always be appropriate. In other words, in the construction work, it is possible to work in a state where a small amount of groundwater is allowed to flow from the bottom, and it is safe even if the working air pressure is lower than the working air pressure obtained by calculation based on many achievements. And it has been demonstrated that proper work is possible.

With reference to FIG. 4, the working atmospheric pressure of the construction work in Dotan will be described. As shown in FIG. 4, when the caisson construction target ground is Dotan, the natural pressure p ′ is generated on the ground, and the working pressure P _w is appropriately about 0.7 times p ′. It becomes pressure. In this state, since the amount of groundwater flowing from the bottom is small, no problem occurs in the implementation.

In addition, as described above, the amount of groundwater flowing into the caisson work chamber changes according to the hydraulic conductivity of the construction ground. That is, as shown in FIG. 5, the air permeability coefficient is smaller the larger the permeability, the permeability is permeability coefficient becomes larger the smaller. The hydraulic conductivity depends on the degree of saturation. Therefore, the working air pressure can be set lower than the predetermined planned value by appropriately managing the saturation of the construction ground.

  The present invention has been proposed in view of the above-described circumstances, and by appropriately managing the saturation of the construction ground, it is possible to set the working air pressure lower than a general plan value and increase the working efficiency. It aims to provide a new pneumatic caisson method.

The pneumatic caisson method according to the present invention has been proposed to achieve the above-described object, and has the following features. That is, in the pneumatic caisson method according to the present invention, prior to caisson settling, a plurality of sets of airpipes with different depths of the air inlets are set in the surrounding ground where the caisson is set. Insert air supply pipes at multiple locations. Then, the ground is desaturated by injecting gas into the ground at a pressure corresponding to the depth of the air supply port, and the amount of groundwater flowing into the caisson work chamber is reduced.

In addition, the pneumatic caisson method according to the present invention has a plurality of air inlets with different depths along the length direction at a plurality of locations in the surrounding ground where the caisson is set, prior to the caisson setting. Insert the airpipe you have. Then, the ground is desaturated by injecting gas into the ground at a pressure corresponding to the depth of the air inlet from the air inlet selected according to the depth of the ground, and the amount of groundwater inflow into the caisson work chamber It is characterized by reducing.

In the above-described pneumatic caisson method, it is preferable to inject gas into the ground while increasing the gas pressure to be supplied as the depth of the air supply port increases.

  According to the pneumatic caisson method according to the present invention, prior to the caisson settling, the ground is desaturated by injecting gas into the ground, and the working pressure is set lower than the general planned value. It becomes possible to increase work efficiency.

Explanatory drawing of the pneumatic caisson method which concerns on the 1st Embodiment of this invention. Explanatory drawing of the pneumatic caisson method which concerns on the 2nd Embodiment of this invention. Explanatory drawing of the pneumatic caisson method which concerns on the 3rd Embodiment of this invention. Explanatory drawing of the working | atmospheric pressure in an implementation construction. Explanatory drawing which shows the relationship between a saturation, a water permeability coefficient, and a gas permeability coefficient.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1-3 is explanatory drawing of the pneumatic caisson method which concerns on embodiment of this invention. FIG. 4 is an explanatory diagram of the working air pressure in the construction work, and FIG. 5 is an explanatory diagram showing the relationship between the degree of saturation, the water permeability coefficient, and the air permeability coefficient.

  In the pneumatic caisson method according to the embodiment of the present invention, as shown in FIGS. 1 to 3, prior to the caisson 10 being set, the ground is desaturated by injecting gas into the ground, and the caisson work is performed. The amount of groundwater flowing into the room is reduced, and an air supply pipe 20 having an air supply port 21 is inserted into the surrounding ground where the caisson 10 is set, and as the depth of the air supply port 21 increases, The gas is injected into the ground while increasing the gas pressure.

  The air supply pipe 20 may be of any material and shape as long as it can be inserted into the ground. For example, a cylindrical steel pipe can be used. In addition, an air supply port 21 is provided in the air supply pipe 20, and an air supply pump 30 for supplying gas (for example, air) having a predetermined pressure is connected in communication. In addition, the air supply pressure can be adjusted by providing the pressure adjusting valve 40 between the air supply pump 30 and the air supply pipe 20. Further, when a plurality of air supply pipes 20 are present, by providing a switching valve (not shown) between the air supply pump 30 and the air supply pipe 20, it is possible to switch the air supply pipe 20 that supplies air. . Hereinafter, specific embodiments will be described.

<First Embodiment>
In the first embodiment, as shown in FIG. 1, a plurality of air feeding tubes 20 having different depths of the air feeding ports 21 are inserted into the surrounding ground where the caisson 10 is set. Each of the air supply pipes 20 is provided with, for example, an air supply port 21 in the vicinity of the distal end portion to be inserted into the ground. The thickness of the air supply pipe 20, the size of the air supply opening 21, the position where the air supply opening 21 is provided, the number of the air supply openings 21, and the air supply pressure depend on the soil condition of the ground where the caisson 10 is set, the surrounding environment, and the like. It implements by changing suitably (same in 2nd Embodiment and 3rd Embodiment).

  And by injecting gas into the ground at a pressure corresponding to the depth from the air inlet 21 of each air pipe 20 and desaturating the ground, the desaturation is reliably performed according to the depth of the ground. be able to. If the ground is desaturated, the hydraulic conductivity will decrease, and even if the air supply pressure to the caisson work room is set lower than the general plan value, the ingress of groundwater into the caisson work room will be controlled appropriately. (Similar in the second embodiment and the third embodiment).

<Second Embodiment>
In the second embodiment, as shown in FIG. 2, an air supply pipe 20 having a plurality of air supply ports 21 is inserted in the surrounding ground where the caisson 10 is set. The air supply tube 20 according to the second embodiment is configured such that the packer 50 is inserted therein. The packer 50 is made of a bag-like member (for example, a rubber bag) having flexibility and flexibility. In addition, a pipe 51 for inflating the packer 50 by injecting liquid (for example, water) or gas (for example, air) into the packer 50 is connected to the packer 50. In addition, a pump 52 and a pressure adjustment valve 53 for sending liquid or gas into the packer 50 are connected to the pipe 51 in communication.

  Then, the packer 50 in a contracted state is inserted at a desired depth, and the inside of the packer 50 is filled with liquid or gas through the pipe 51, so that the outer periphery of the packer 50 is in close contact with the inner surface of the air supply pipe 20. The trachea 20 can be sealed. In this state, by supplying air into the air supply pipe 20 below the packer 50, the air supply port 21 selected according to the depth of the ground from the air supply port 21 into the ground at a pressure corresponding to the depth of the air supply port 21. A gas can be injected. In order to supply air into the air supply pipe 20 below the packer 50, an air supply pipe (not shown) is inserted into the air supply pipe 20, and the insertion position (insertion depth) of the ventilation pipe is adjusted. That's fine.

  Further, by extracting the liquid or gas from the inside of the packer 50 through the pipe 51, the outer peripheral portion of the packer 50 is detached from the inner surface of the air supply tube 20, and the packer 50 can be moved.

  Note that only one packer 50 may be used. In this case, gas is injected into the ground from the air supply port 21 located immediately below the packer 50. In the example shown in FIG. 2, a pair of upper and lower packers 50 are provided, and both packers 50 are filled with liquid or gas to close a section sandwiched between both packers 50, and the air supply port of the closed section The gas is injected from 21 into the ground.

<Third Embodiment>
In the third embodiment, as shown in FIG. 3, in the surrounding ground where the caisson 10 is set, the air supply port 21 is positioned below the set position of the caisson 10 as the caisson 10 is set. In this way, the air supply tube 20 is inserted. That is, prior to the caisson 10 being set, the insertion depth of the air supply pipe 20 is sequentially changed so that the air supply port 21 is located below the caisson 10 setting position, and the ground where the caisson 10 is set in advance is set. Is desaturated. At this time, gas is injected into the ground at a pressure corresponding to the depth of the air supply port 21.

<Working pressure>
As described above, the working air pressure is about 0.7 times the natural water pressure p ′. However, in the present invention, since the ground is desaturated when the caisson 10 is laid, a general plan is used. Even if the working air pressure is set lower than the value, safe and appropriate work can be performed.

10 caisson 20 air supply pipe 21 air supply port 30 air supply pump 40 pressure regulating valve 50 packer 51 pipe 52 pump 53 pressure regulating valve

Claims (3)

Prior to caisson settling, in the surrounding ground where the caisson is set up, a plurality of air pipes with different depths of the air inlets are set as one set, and multiple sets of air pipes are inserted at multiple locations,
From the air inlet of each air pipe, the ground is desaturated by injecting gas into the ground at a pressure according to the depth of the air inlet,
Pneumatic caisson method characterized by reducing the amount of groundwater flowing into the caisson work room. Prior to the caisson laying, the air feeding pipe having a plurality of air feeding ports having different depths along the length direction is inserted into a plurality of locations in the surrounding ground where the caisson is sunk,
From the air inlet selected according to the depth of the ground, the ground is desaturated by injecting gas into the ground at a pressure according to the depth of the air inlet,
Pneumatic caisson method characterized by reducing the amount of groundwater flowing into the caisson work room. Injecting gas into the ground while increasing the gas pressure to be supplied as the depth of the air supply port increases,
The pneumatic caisson method according to claim 1 or 2.

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