JP2920802B2 - Ground improvement method just below the existing structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground improvement method for improving the foundation of an existing structure such as a building or an existing tank.

[0002]

2. Description of the Related Art In general, measures for preventing liquefaction of the ground include:
For example, a method is known in which the ground is compacted with a sand pile placed in the ground, or a method in which excessive pore water pressure generated during an earthquake is rapidly dissipated by a pipe having good permeability and penetrated into the ground.

[0003]

The above-mentioned countermeasures against liquefaction of the ground have the following problems.

<A> Although these liquefaction prevention measures described above are effective for the ground before the construction of the structure, it is extremely difficult to apply it to the improvement of the direct foundation of the existing structure. It is.

<B> The method of fastening with a sand pile cannot be adopted when there is an existing structure in the vicinity.

<C> LNG which is currently expected to be liquefied
There are important existing structures such as tanks and LPG tanks.
Thus, it is urgently necessary to propose and implement measures to prevent liquefaction in important existing structures.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a structure directly under an existing structure which can be easily constructed without any adverse effect on the existing structure. It is to provide a ground improvement method.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for improving the ground immediately below an existing structure, the method comprising the steps of reaching from a ground around the existing structure to an opposite side of the existing structure through immediately below the existing structure. The first is to arrange the arc-shaped pilot pipes in parallel.
Steps and attaching a widening bit having a function of discharging the consolidated material to the end of each pilot pipe, and agitating the consolidated material and the ground with the widened bit in parallel with the removal of the pilot pipe and directly below the existing structure And a second step of constructing an impermeable layer that defines the ground. A method of improving the ground immediately below an existing structure. Further, the present invention provides a method for improving the ground immediately below an existing structure, wherein an arc-shaped pilot pipe is arranged so as to reach the opposite side of the existing structure from immediately below the existing structure through the ground immediately below the existing structure. A first step of setting, attaching a widening bit having a function of discharging a consolidated material to the tip of each of the pilot pipes, and stirring the consolidated material and the ground with the widened bit in parallel with extracting the pilot pipe. It is characterized by comprising a second step of constructing an arc-shaped impermeable layer immediately below a structure and a third step of constructing vertical water blocking walls adjacent to both sides of the arc-shaped impermeable layer. This is the ground improvement method immediately below the existing structure. Further, the present invention provides a method for improving the ground immediately below an existing structure, wherein an arc-shaped pilot pipe is arranged so as to reach from the ground near the existing structure to the opposite side of the existing structure immediately below the existing structure. A first step of setting, attaching a widening bit having a function of discharging a consolidated material to the tip of each of the pilot pipes, and stirring the consolidated material and the ground with the widened bit in parallel with extracting the pilot pipe. A second step of constructing a water-impermeable layer that defines a base ground of the structure, and a third step of draining by installing a drain hole in the inner ground defined by the water-impermeable layer This is a ground improvement method directly below the existing structure.

[0009]

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings.

<A> Pilot Pipe Penetration Process (FIG. 2) An existing structure 2 is erected on a ground 1 such as a sandy ground or a soft ground. The arc-shaped pilot pipe 3 is penetrated into the ground so as to cross the bottom of the existing structure 2, and the tip of the pilot pipe 3 reaches the opposite side of the penetrating position across the existing structure 2. The pilot pipe 3 is composed of a plurality of divided pipes having a plurality of arc diameters. In order to drive the rotary bit 31, a flexible transmission shaft 32 continuously inserted into the pilot tube 3 as shown in FIG.
The rotation bit 31 may be connected to the distal end of the transmission shaft 32 to apply rotation from the proximal end side of the transmission shaft 31. In this way, a plurality of pilot pipes 3 are juxtaposed so as to cross right below the existing structure 2.

<B> Attaching the Widening Bit 5 (FIGS. 3 and 4) When the tip of the pilot tube 3 reaches the opposite side of the existing structure 2, a hollow structure inserted into the pilot tube 3 as shown in FIG. The widening bit 4 is attached to the transmission shaft 32 via a bearing 33. The widening bit 4 has a stirring blade 41 having a diameter larger than that of the pilot tube 3 and has a discharge hole 42 formed in the axis thereof.

<C> Ground improvement step (FIGS. 1 and 3) Next, while pulling back the pilot pipe 3, a cement such as cement paste is discharged from the base end of the transmission shaft 31 from the tip end of the widening bit 4 and simultaneously widened. Excavation and agitation with bit 4 to improve the ground. Similar ground improvement is continuously performed while successively pulling back each adjacent pilot pipe 3, and finally, an arc-shaped plate-shaped water-impermeable material is obtained by continuous ground improvement across the base ground of the existing structure 2 as shown in FIG. Build layer 6.

<D> Auxiliary water blocking wall work (FIG. 1) Next, a vertical water blocking wall 7 which is in contact with both ends of the circular plate-shaped impermeable layer 6 is constructed. The vertical water blocking wall 7 is constructed by a known sheet pile method, a continuous underground wall method, or the like. As a result, the base plate of the existing structure 2 is isolated by the impermeable layer 6 and the vertical water blocking wall 7. A large number of pilot pipes 3 are arranged so as to surround the entire periphery of the existing structure 2 and a mortar-shaped impermeable layer 6 is formed.
Is formed, the vertical water blocking wall 7 can be omitted.

<E> Action As shown in FIG. 1, if the base layer of the existing structure 2 is separated by the water-impermeable layer 6 and the vertical water blocking wall 7, the outer ground 1 a of the water-impermeable layer 6 is damaged when an earthquake occurs. Even if it vibrates, this vibration is not transmitted to the inner ground 1b of the isolated impermeable layer 6, and as a result, an increase in pore water pressure of the inner ground 1b directly supporting the existing structure 2 can be avoided.

[0015]

[Embodiment 2] FIG. 5 shows that an arc-shaped drain hole 8 is constructed above the arc-shaped impermeable layer 6 constructed in the same manner as in the first embodiment, and a submersible pump 81 is provided in the drain hole 8. An example in which is arranged is shown. The drain hole 8 is installed by connecting an arc-shaped drain pipe, or a straight drain pipe is used, and is arranged in a substantially V-shape so as to intersect immediately below the structural part of the existing structure 2. In the present embodiment, the inner ground 1b partitioned by the impermeable layer 6 by operating the submersible pump 81
There is an advantage that the effective stress of the inner ground 1a immediately below the existing structure 2 can be increased by lowering the underground water level of the existing structure 2.
The drain hole 8 can be a known drain pipe or the like. Embodiments 1 and 2 described above are effective when the target ground where liquefaction is expected exists to a large depth.

[0016]

[0017]

As described above, the present invention has the following effects.

<A> An arc-shaped plate-shaped water-impermeable layer can be constructed for a directly underlying base plate of an existing structure, for which liquefaction prevention measures have heretofore been considered difficult.

<B> Since the work is performed around the existing structure so far, there is no fear that the existing structure is adversely affected.

<C> Even when the target ground where liquefaction is expected extends to a large depth, the liquefaction of the ground can be effectively prevented.

<D> By providing a drain hole above the water-impermeable layer and draining water, the effective stress of the base plate of the existing structure can be increased.

<E> When the impermeable ground exists in a relatively shallow range, the surrounding structure of the existing structure is surrounded by a vertical water blocking wall, and a drain hole is provided just below the existing structure. Construction can prevent liquefaction of the base plate of the existing structure.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment according to the present invention.

FIG. 2 is an explanatory diagram of a pilot pipe penetration process.

FIG. 3 is an explanatory diagram of a step of constructing an impermeable layer.

FIG. 4 is an explanatory view of an attached state of a widening bit.

FIG. 5 is an explanatory view of a second embodiment.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-134441 (JP, A) JP-A-52-33308 (JP, A) JP-A-64-14417 (JP, A) 47395 (JP, A) JP-A-2-80789 (JP, A) JP-A-2-80790 (JP, A) JP-A-63-236823 (JP, A) JP-A-4-131427 (JP, A) JP-A-4-213613 (JP, A) JP-B-51-47252 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) E02D 27/48 E02D 3/10 101 E02D 3 / 12 102 E02D 27/34

Claims (3)

(57) [Claims] In a method for improving the ground immediately below an existing structure, an arc-shaped pilot pipe is arranged so as to reach the opposite side of the existing structure from immediately below the existing structure through the ground immediately below the existing structure. A first step of installing, attaching a widening bit having a function of discharging a consolidated material to the tip of each of the pilot pipes, and agitating the consolidated material and the ground with the widened bit in parallel with extracting the pilot pipe. Second construction of impermeable layer that defines the direct foundation of the structure
The ground improvement method immediately below the existing structure, characterized by the process. 2. A method for improving the ground immediately below an existing structure, wherein a pilot pipe having an arc shape is arranged so as to reach the opposite side of the existing structure from immediately below the existing structure through the ground immediately below the existing structure. A first step of installing, attaching a widening bit having a function of discharging a consolidated material to the tip of each of the pilot pipes, and agitating the consolidated material and the ground with the widened bit in parallel with extracting the pilot pipe. It is characterized by comprising a second step of constructing an arc-plate-shaped impermeable layer immediately below a structure, and a third step of constructing vertical water blocking walls adjacent to both sides of the arc-plate-shaped impermeable layer. The ground improvement method immediately below the existing structure. 3. A method for improving the ground immediately below an existing structure, wherein a pilot pipe having an arc shape is arranged so as to reach the opposite side of the existing structure from immediately below the existing structure through the ground immediately below the existing structure. A first step of installing, attaching a widening bit having a function of discharging a consolidated material to the tip of each of the pilot pipes, and agitating the consolidated material and the ground with the widened bit in parallel with extracting the pilot pipe. Second construction of impermeable layer that defines the direct foundation of the structure
And a third step of draining and installing drain holes in the inner ground defined by the water-impermeable layer, wherein the ground is improved immediately below the existing structure.