JP2000336669A - Liquefaction countermeasure construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquefaction countermeasure construction method excellent in adaptability to a circular foundation to prevent the liquefaction of the ground, scarcely limited in ground improvement depth to reduce its improvement rate and excellent in adaptability to piles disposed in ring shape. SOLUTION: The liquefaction preventive ground A with a plurality of cylindrical impermeable walls 4 disposed concentrically from the top view is formed in the ground 1 with the possibility of liquefaction, and a structure 6 is constructed on the ground A. The structure 6 can therefore be constructed while exhibiting above-mentioned excellent characteristics by the ring effect of the liquefaction preventive ground A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing liquefaction, and more particularly to a method suitable for constructing structures on a tank foundation, a plant foundation, a building foundation, a bridge foundation, a tower foundation, etc. having a circular foundation. The present invention relates to a liquefaction-prevention method capable of reducing liquefaction damage directly below or around the ground.

[0002]

2. Description of the Related Art As a measure for preventing liquefaction of soft ground, it has been proposed to construct an underground closed wall around a directly grounded foundation of a structure, and to employ an enclosing foundation formed of the underground closed wall with a water-permeable material. (Japanese Patent Publication No. 3-28534).

[0003] The surrounding foundation is constructed such that moisture in the ground below the surrounding structure is sucked into a permeable surrounding foundation in the event of an earthquake or the like and rises, and drainage is dissipated from the upper end thereof. It is intended to prevent the liquefaction by suppressing the rise of the internal water pressure and to stably maintain the ground, but as the size of the structure increases, the volume of the soft ground immediately below the structure increases The effect is weakened, which is inappropriate as a reliable liquefaction prevention measure.

As a good liquefaction prevention measure for solving such inconveniences, the present applicant has previously proposed a high horizontal proof strength basic construction method using a solidification method (Japanese Patent No. 2645899) and a TO method.
The FT method (trademark registration No. 3107839) has been proposed. In this method, a stabilizer is stirred and mixed in a ground that may be liquefied by a deep mixing machine to form a flat lattice-like water-impermeable wall structure that reaches from the lower end to the upper end of the ground. In addition, a foundation pile is constructed by penetrating a lower end of a plurality of ground portions surrounded by a lattice-like portion of the impervious water-permeable wall structure to a ground that has a supporting force below the ground and does not liquefy. .

According to this method, as shown in FIG. 9, the improved ground B is formed together with the unconsolidated ground portion left in the lattice-shaped portion 10, so that the rigidity of the whole ground is reduced by the support under the ground. It will be raised to about the same level as the ground,
Therefore, the horizontal displacement during an earthquake can be significantly reduced as compared to the ground around the improved ground, and the liquefaction during the earthquake can be reliably prevented in the ground portion within the impermeable wall structure. Therefore, no liquefaction destruction occurs in the improved ground, and the ground part in the grid-like part of the impervious wall structure has high support of the foundation pile without consolidation by the small compartment. As a result, it is possible to construct individual pile foundations having a small horizontal displacement and a large horizontal and vertical proof stress at the time of an earthquake without any trouble.

[0006]

The above-mentioned foundation method, which has the above-mentioned excellent characteristics, has a flat grid-like structure as a measure for preventing liquefaction against seismic motion acting in all directions of the foundation (360 ° in all directions). The aspect ratio (soil improvement interval / soil improvement depth) of the vertical and horizontal is approximately equivalent, and the plane length of these vertical and horizontal bulkheads has a certain degree of absolute value for obtaining sufficient strength and liquefaction prevention effect. Because of the limitation, the number of partitions effective for preventing liquefaction is surely increased in proportion to the size of the structure.

In addition, as for the substantially equivalent vertical and horizontal lengths of the grid-like ground improvement, the minimum absolute value is limited to some extent as described above, so that the ground improvement rate (ground improvement area / There is a limit to the reduction of the ground improvement area).

In some cases, the piles used as the support members for the circular foundation are arranged in a ring shape. In such a case, if the ground improvement portion is in a lattice shape, it is difficult to arrange the ground improvement portion in an appropriate ring-shaped position. Therefore, grid-based ground improvement is structurally superior and economical in preventing liquefaction of linear structures such as buildings and seawalls, which are often box-shaped, but is suitable for circular foundations such as tanks. Hard to say.

The present invention has been made in view of the above points, and it is possible to prevent the liquefaction of the ground as well as to limit the ground improvement depth and to provide a wide adaptability to the target structure. , The rate of improvement can be reduced,
The present invention proposes a liquefaction prevention countermeasure method that is excellent in adaptability to ring-shaped piles.

[0010]

In order to solve the above-mentioned problem, a method for preventing liquefaction according to the present invention comprises providing a plurality of cylindrical water-impermeable walls in a ground which may be liquefied. The liquefaction-preventing ground disposed concentrically in a plan view is formed by a deep-layer mixing method, and a structure is constructed on the ground to constitute a liquefaction-preventing countermeasure method.

The construction method according to the second aspect of the invention is a construction method for preventing liquefaction according to the first aspect, wherein the surface layer between upper portions of the impervious walls has a solid reinforcement structure.

According to a third aspect of the present invention, there is provided a method for preventing liquefaction, wherein a radial partition is formed on a surface layer between upper portions of each impervious wall by using a mixing method. It was constituted as.

[0013]

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

The liquefaction-prevention method of the present invention forms a liquefaction-preventive ground in which a plurality of cylindrical impervious water-permeable walls are concentrically arranged in a liquefiable ground. A structure is constructed on the ground.

In the illustrated example, a ground 1 is a ground that may be liquefied, and a ground 2 exists below the ground.
Is formed of a ground such as a clay layer which is unlikely to be liquefied. Further, a supporting ground 3 such as a rock exists below the ground 2. A liquefaction-preventing ground A composed of a plurality of impervious walls 4 is formed on the ground 1, and a structure 6 such as a tank is constructed on the ground 1 via a foundation slab 5.

The liquefaction-preventing ground A according to the present invention is prepared by mixing and dispersing a stabilizer such as cement at a target site of the ground to form a hardened water-permeable treatment site having a higher rigidity. It is formed using a processing method, and to give a more specific example, using a deep mixing machine, a slurry prepared by mixing a stabilizer or the like and a stabilizer and water at an appropriate ratio is ground. 1 to form a plurality of impervious walls 4 arranged concentrically in a plan view, each impervious wall 4 ... and a ground portion surrounded by each impervious wall 4. so,
The liquefaction prevention ground A is formed.

The number, width, depth, and the like of the water-impermeable walls 4 in the liquefaction-preventing ground A can be appropriately selected according to the form and size of the structure to be constructed. In the present invention, since the impervious walls 4 are cylindrical and have a plurality of concentric circles, they are structurally superior in reducing shear stress and excess pore water pressure as compared with the grid-like improved ground. It is possible to reduce the ground improvement rate which is the minimum necessary for liquefaction countermeasures, and it can be expected that the effect of reducing the ground improvement rate for grid-like ground improvement can be expected.

Further, in order to further improve the rigidity of the liquefaction prevention ground A effective for the liquefaction prevention effect, a solid reinforcement structure 7 is provided between the upper portions of the water-impermeable walls 4 as shown in FIGS. It is also possible. Specific examples of the reinforcing structure 7 include:
A method in which the upper portion of the impervious wall 4 is filled with a material such as crushed stone or concrete, or a method in which the surface ground is made into a rigid surface ground by a mixing method or the like.

For the same purpose, as shown in FIGS. 5 and 6, a radial partition 8 may be formed between the upper portions of the water-impermeable wall 4 by using a mixing method.

The structure 6 includes tanks, plants, buildings,
Anything such as bridges and towers can be applied, but more preferably those with a circular foundation. Further, the structure 6 may be directly constructed on the liquefaction-preventing ground via, for example, a foundation slab, or may be constructed via a foundation slab on a foundation pile penetrated in the liquefaction-preventing ground. good.

FIGS. 7 and 8 show that a predetermined number of foundation piles 9 are constructed by penetrating the lower end of the ground 2 below the ground 1, a foundation slab 5 is provided at the top end of the foundation pile 9, and Shows an example in which the structure 6 is constructed. The foundation pile 9 is also applied to the case of the liquefaction-preventing ground provided with the above-mentioned solid reinforcement structure 7 or the partition 8, but in this case, the solid reinforcement or the partition construction may be performed after the foundation pile 9 is constructed.

As described above, the structure is built directly on the liquefaction-preventing ground via a foundation slab or connected to the upper end of a foundation pile. Acting on the ground and the foundation pile, the displacement against the horizontal force as the whole foundation is much smaller than when there is no liquefaction prevention ground, and when the foundation pile is present, the horizontal force shared by the pile Is much smaller than with only a stake.

[0023]

As described above, the method for preventing liquefaction of the ground according to the present invention has the above-described structure, and is improved together with the unconsolidated ground portion remaining between the cylindrical water-impermeable walls. Since the ground is formed, the rigidity of the entire ground is increased to substantially the same level as the supporting ground below the ground. Therefore, the horizontal displacement during the earthquake can be significantly reduced compared to the ground around the improved ground, and the liquefaction during the earthquake in the ground part in the liquefaction prevention ground can be surely suppressed, Moreover, liquefaction prevention measures suitable for an arbitrary circular basic shape can be taken.

Further, since each impervious wall is cylindrical,
In addition, the liquefaction-prevention ground has a plurality of these ring-shaped impervious walls, which has the structural advantage of reducing ground shear stress and excess pore water pressure, and also limits the ground improvement depth. By adjusting the number and spacing of the impervious walls to a small extent, it is possible to set the minimum ground improvement rate required for liquefaction prevention measures, and it is possible to implement liquefaction prevention measures with excellent economic efficiency.

Further, according to the present invention, when the piles used as the support members of the foundation are arranged in a ring shape, the piles can be easily fitted in the liquefaction-preventing ground, and the structure construction process can be carried out smoothly. You can proceed.

In the case where the surface ground between the upper portions of the impervious walls has a solid reinforcement structure, or the case where a radial partition is formed by using a mixing method, it is effective in preventing liquefaction. The rigidity of the liquefaction-preventing ground can be further improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a structure formed according to the present invention.

FIG. 2 is a transverse sectional view of a liquefaction target layer portion of the embodiment.

FIG. 3 is a longitudinal sectional view showing another embodiment of the structure formed according to the present invention.

FIG. 4 is a cross-sectional view of a portion to be liquefied according to the embodiment.

FIG. 5 is a longitudinal sectional view showing still another embodiment of the structure formed according to the present invention.

FIG. 6 is a cross-sectional view of a liquefaction target layer portion according to the same embodiment.

FIG. 7 is a longitudinal sectional view showing still another embodiment of the structure formed according to the present invention.

FIG. 8 is a cross-sectional view of a liquefaction target layer portion according to the same embodiment.

FIG. 9 is a cross-sectional view of a liquefaction target layer portion of a structure formed by a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ground to be liquefied, 2 ... Non-liquefied ground, 3 ... Support ground, 4 ... Impermeable wall, 5 ... Foundation slab, 6 ... Structure, 7
... solid reinforcement structure, 8 ... partition, 9 ... foundation pile, A ... liquefaction prevention ground

Continuing from the front page (72) Inventor Sadatomo Onimaru 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside the Technical Research Institute, Takenaka Corporation (72) Inventor Ryosuke Okumura 8-2-1-1, Ginza, Chuo-ku, Tokyo Stock Company Takenaka Civil Engineering (72) Inventor Kazuhiko Suzuki 8-21-1, Ginza, Chuo-ku, Tokyo F-term (reference) 2D046 DA03 DA05 DA11 DA17

Claims (3)

[Claims] 1. A liquefaction-preventing ground in which a plurality of cylindrical water-impermeable walls are concentrically arranged in a plan view is formed in a liquefiable ground by a deep-layer mixing method. A liquefaction prevention countermeasure method characterized by building a structure on top. 2. The liquefaction-prevention method according to claim 1, wherein the surface ground between the upper portions of the impervious walls has a solid reinforcement structure. 3. The method for preventing liquefaction according to claim 1, wherein a radial partition is formed in the surface ground between the upper portions of the respective impervious walls using a mixing method.