JPH047779B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for constructing an underground structure that can be constructed at great depths, and is designed to be applicable even in urban areas with soft ground.

[Conventional technology]

Conventionally, as a method for constructing an underground framework when the construction depth is large or when the underground water level is high and there is a risk of heaving, boiling, etc., for example, the pneumatic caisson construction method using compressed air has been used. In that case, a structure frame with a cutting edge on the outer periphery of the pressure plate at the lower end is constructed one after another on the ground, and excavation is carried out manually in a work room under the pressure plate, which is pressurized to counter groundwater pressure. The method used is to deposit them in stages.

Construction of such underground structures using caisson requires that the frame be vertically and precisely sunk to a predetermined depth. However, there is a risk that it may become difficult to sink due to frictional forces between the frame surface and the ground, and construction may become difficult due to occurrence of boiling, heaving, etc. In addition, loading to encourage subsidence,
In the case of pneumatic caissons, there are methods to temporarily lower the pressure, but it is difficult to control the sinking.

In addition, in the case of the open caisson construction method, underground water pressure can usually be dealt with by underwater excavation, etc., but if there is large water pressure, heaving and boiling may occur, which may also affect the surrounding ground, such as subsidence. . Furthermore, with the open caisson construction method, the slabs for each floor must be constructed later, which has the problem of affecting the construction process.

In addition, as a construction method to solve these problems, the applicant places jacks on the frame of a structure built on the ground, excavates under the frame, and uses a reaction force on the earth anchor to lower the frame into the ground. An application has already been filed regarding the method of pushing and sinking (Japanese Patent Application No. 243679/1982). This construction method allows the building to be lowered while controlling the sinking speed and correcting the slope, and also allows the earth anchor to be used as a measure against building buoyancy.

[Problem that the invention seeks to solve]

When the structure is filled with fresh water or muddy water as a submerged load and the structure is sunk while excavating underwater, the fresh water or muddy water inside is discharged after the structure has been sunk to a predetermined depth. By the way, when fixing the anchor member head of the main earth anchor for buoyancy countermeasures to the bottom plate of the structure, it is necessary to first drain the fresh water or muddy water inside the structure, but in order to do this, the underground water level must be lowered with a deep well etc. It is necessary to take measures such as lowering the temperature. However, pumping up groundwater has an impact on the surrounding ground, so it must be minimized as much as possible.

This invention aims to solve the above-mentioned problems.

[Means for solving problems]

In the construction method of this invention, the framework built on the ground is filled with fresh water or muddy water to resist buoyancy.
The area will be excavated below the bottom slab and deposited in stages. Ground anchors for buoyancy countermeasures will be placed at multiple locations on the slab that makes up the bottom slab, and if necessary, the earth anchors penetrating the walls of the building structure will be used to absorb reaction force and reduce the sinking speed, inclination, etc. by means of jacking, etc. It will be installed while being corrected.

For the permanent earth anchors in the center of each slab, once the structure has been sunk to a predetermined depth, a pipe with the anchor member of the earth anchor penetrated from the bottom of the structure is raised above the water while it is filled with fresh water or muddy water. An anchor member is temporarily attached at the top to counteract buoyancy. After that, clean water or muddy water inside the frame is removed, the anchor member is fixed to the bottom plate, and unnecessary parts are cut off.

〔Example〕

Next, the illustrated embodiment will be described.

FIG. 1 shows a state in which a frame 1 is tentatively attached by earth anchors 5 in the process of the present invention. In addition, the left half of the figure shows a state in which after temporary landing, the groundwater level in one part of the frame was lowered by the deep well 14, and the fresh water or muddy water 8 inside was discharged.

An underground continuous wall 13 that serves as earth retaining and water stop is constructed in advance around the submerged position, and has a cutting edge 3 at the lower end, and a bottom plate 2 is used to connect the frame 1 that will be built sequentially on the ground.
The site will be gradually submerged while excavating the area below. Inside the frame 1, there is fresh water or muddy water 8 as a submerged load.
The slab including the bottom plate 2 is provided with a through hole 4 through which an anchor member (PC strand 7) of an earth anchor 5 for buoyancy countermeasures is passed.

After the frame 1 has been sunk to a predetermined depth, underwater concrete 12 is placed under the bottom slab 2, and a pipe 9 such as a steel pipe is raised above the water surface so as to cover the PC strand 7 of the earth anchor 5 on the bottom slab 2. . In this state, the upper end of the PC strand 7 is temporarily attached to the upper end of the pipe 9. Thereby, the frame 1 can resist buoyancy even if fresh water or muddy water 8 is discharged from inside.

In addition, 15 in the figure is a water stop device to prevent groundwater from entering from the earth anchor through hole 4 of the bottom plate 2 at an early stage, as will be described later. At the same time, the PC strand 7 can be fixed at the upper position of the bottom plate 2 while the water stop device 15 is activated to eliminate water inside the frame 1. Note that the water stop device 15 is particularly effective in preventing the intrusion of pressurized groundwater rising from below the impermeable layer b along the earth anchor 5 even if the groundwater level is lowered by the deep well 14 or the like. .

Figures 2a and 2b show an example of the structure of the water stop device 15, in which a sheath 16 has a plurality of PC strands 7 passed through the earth anchor 5, and a pipe with a diameter larger than the sheath 16 is inserted in the middle of the earth anchor 5. Storage part 1
7 is attached, and a waterproof packer 18 consisting of a bag surrounding the PC strand 7 in a donut shape is attached to the packer storage part 17. The water stopper 18 is made of rubber-lined cloth, rubber, plastic, etc., and has a grout tube 21 at the bottom for feeding grout material from the ground, and an air vent tube at the top, which is operated by air or water pressure to temporarily release the water. Water can be stopped, and when performing the actual water stopping, the water stopping packer 18 is inflated by grout injection and brought into close contact with the PC strand 7. Also
For the space between 7 PC strands, place rubber or plastic on the top and bottom of the water stop section in advance.
By attaching a water stop spacer 19 made of metal or the like and filling the space with a filler 20 such as silicone rubber, the spacer is pressed by the swollen water stop spacer 18.
Groundwater intrusion is prevented. The structure of the water stop spacer and the number of spacers that come into contact with the water stop spacer 18 are changed depending on the magnitude of the groundwater pressure. If it is minor, use at least one star-shaped spacer water stopper 1
8 should be brought into contact with it.

〔Effect of the invention〕

In the construction method of this invention, the pipe is raised above the water from the bottom plate of the structure while the inside of the submerged structure is filled with fresh water or muddy water as a submerged load, and the permanent earth anchor, which is fixed to the slab of the bottom plate, is temporarily attached to the top end of the pipe above the water. After the ground anchor is installed, clear water or muddy water is discharged to perform the final fixation of the earth anchor, so construction can be carried out in a stable state over the entire construction period, and there is less lowering of the groundwater level due to deep wells, etc., so it does not affect the surrounding ground. There is little worry about negative effects.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIGS. 2a and 2b are a vertical sectional view and a horizontal sectional view, respectively, of a water stop device. 1...Main body, 2...Bottom plate, 3...Blade mouth, 4...
Through hole, 5...Earth anchor, 6...Fixing part,
7...PC strand, 8...Clear water or muddy water,
9... Pipe, 10... Temporary attachment part, 12... Underwater concrete, 13... Underground continuous wall, 14... Deep well, 15... Water stop device, 16... Sheath, 17... Police car storage section , 18... Water stop packer, 19... Water stop spacer, 20... Filler, 21... Grout tube, 22... Air vent tube, a... Groundwater level, b... Impermeable layer.

Claims (1)

[Claims] 1. In this method of constructing underground structures, the structure constructed above ground is filled with fresh water or muddy water to counteract buoyancy, while the bottom slab is excavated and the structure is sunk one after another.When the structure is sunk to a predetermined depth, it is grounded from the bottom slab of the skeleton. A pipe passing through the anchor member of the anchor is raised above water, the anchor member is temporarily attached to the upper part of the pipe, fresh water or muddy water inside the frame is removed, and then the anchor member is fixed to the bottom plate. How to construct an underground structure.