JPH0726545A - Ground structure of existing fabric - Google Patents

Abstract

PURPOSE:To prevent fabric from toppling and collapsing due to ground liquefaction by driving crushed stone drain posts into the ground in the manner of encircling the outer side of strength members driven into the ground in the manner of enclosing an existing fabric. CONSTITUTION:As strength members 3, steel sheet piles are successively driven into the ground 2 of an existing fabric 1 not provided with a liquefaction countermeasure in an manner of enclosing the existing fabric 1. Crushed stone drain posts 4 are driven in an enclosing manner of the steel sheet piles. In other words, crushed stone drain posts 4 are driven into the ground by piercing them into the ground to a specified depth and pulling a casing up after filling it with crushed stone thrown from the top side. A wall of cruched stone drain posts 4 may be formed by bringing them close together. Shearing deformation, which can be the cause for liquefaction, can be restrained by the rigidity of the strength member 3. On the other hand, increase of excessive gap water pressure can be restrained by the discharge effect of the crushed stone drain posts 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground structure of an existing structure which is newly constructed to prevent the ground from being liquefied by taking measures against the liquefaction of the ground.

[0002]

BACKGROUND OF THE INVENTION Liquefaction of the ground is a phenomenon in which the ground is subjected to repeated shear deformation in a substantially non-drained state due to earthquake motion, and the ground becomes close to liquid due to an increase in excess pore water pressure.
Especially easy to occur on loose sand. When liquefaction of the ground occurs, it is likely to cause a major disaster such as the fall and collapse of the structure above it.

On the other hand, some structures such as oil tanks do not have liquefaction countermeasures on the ground depending on the construction time, and those existing structures have new liquefaction prevention measures. It is important to prevent structures from falling or collapsing due to liquefaction of the ground.

A compaction method such as sand compaction is known as a general countermeasure method against the liquefaction of the ground. Sandy material such as sand and gravel is pressed into the ground by vibration load to form a compaction pile. However, this method causes deformation and large vibration of the ground during construction,
Any nearby structures will adversely affect them. Therefore, this method is not suitable for new construction on existing structures.

A steel sheet pile ring construction method has been proposed as a construction method for preventing liquefaction of the ground in an existing structure. In this, as shown in FIG. 3, a steel sheet pile 13 is driven in a ring shape on the surrounding ground 2 so as to surround the existing structure 1,
There is no problem of ground deformation or large vibration during construction.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the ground structure constructed by the conventional steel sheet pile ring construction method proposed as a method for preventing liquefaction of the ground for existing structures, the ground inside the ring of the steel sheet pile is made of steel sheet pile. Rigidity reduces shear deformation and increases resistance to liquefaction, but there is little improvement to the ground outside the ring. Therefore, if the ground on the outer side of the ring is liquefied, the ring itself of the steel sheet pile becomes instable and the resistance effect against liquefaction cannot be exhibited. This is not sufficient as a measure to prevent liquefaction of the ground, and seismic stability of existing structures cannot be maintained.

The present invention has been made in order to solve the above problems, and prevents liquefaction of the ground by newly constructing an existing structure so that sufficient seismic resistance can be maintained. It provides the structure.

[0008]

[Means for Solving the Problems] The above-mentioned problem is solved by driving a strength member such as a steel sheet pile to surround the existing structure on the ground of the existing structure, and crushing a crushed stone drain so as to surround the outside of the strength member. It will be solved by making a ground structure that piles are laid.

Alternatively, the crushed stone drain piles are placed on the ground of the existing structure while crushing the crushed stones, and the individual crushed stone drain piles are placed closely to each other so as to surround the existing structure. It can also be solved by forming a wall.

[0010]

In the ground surrounded by the strength members such as steel sheet piles cast around the existing structure, the rigidity of the strength members suppresses the shear deformation that causes the liquefaction and the resistance against the liquefaction increases. On the other hand, the crushed stone drain pile placed around the strength member has good water permeability, so it has a large drainage effect and suppresses the rise of excess pore water pressure that is the cause of liquefaction, and keeps the strength member in a stable state. can do. This makes it possible to prevent the liquefaction of the ground of the existing structure.

The material and size of the strength member and the size and number of the crushed stone drain piles may be designed based on the seismic response analysis, etc., but the strength member penetrates the liquefied formation on the upper part of the ground and the lower part of the ground. From the viewpoint of stability of the strength member, it is desirable to drive up to the non-liquefied formation, and the crushed stone drain pile may be driven into the formation that is easily liquefied because the drainage property of the formation that is easily liquefied may be improved. In addition, the area where the crushed stone drain pile is placed is 1/2 to 2 / of the depth of the stratum that is liquified easily outside the strength member.
It is preferable to drive up to a region separated by about 3 from the viewpoint of stability of the strength member. The effect is great if the individual crushed stone drain piles are placed in close contact with each other, but they do not necessarily have to be in close contact and may be placed at intervals if the drainage property of the region is improved.

On the other hand, in the case where a crushed stone drain pile is formed while crushing crushed stones around an existing structure to form a wall of the crushed stone drain pile, the ground around the wall of the crushed stone drain pile is solidified by crushing the crushed stones. The shear deformation caused by liquefaction is suppressed and the drainage is improved by the crushed stone drain pile itself, and the increase in excess pore water pressure that is the cause of liquefaction is suppressed. This makes it possible to prevent the liquefaction of the ground of the existing structure.

In this case as well, the dimensions of the individual crushed stone drain piles, the thickness of the entire wall, and the degree of crushing of the crushed stones may be designed based on seismic response analysis, etc., but in order to obtain the compaction effect of the ground. It is necessary to drive the individual crushed stone drain piles in close contact with each other, and the thickness of the entire wall can be about 1/2 to 2/3 of the depth of the liquefiable formation. preferable.

[0014]

EXAMPLE 1 Example 1 of the present invention is shown in FIG. (A) is a top view, (b) is sectional drawing, (c) is an enlarged view of the crushed stone drain pile part of (a). On the ground 2 of the existing structure 1, steel sheet piles are sequentially driven as the strength member 3 so as to surround the existing structure 1, and crushed stone drain piles 4 are driven so as to surround the steel sheet pile. Then, the steel sheet pile penetrates through the liquefiable formation 5 in the upper part of the ground and drives up to the unliquefied formation 6 in the lower part of the ground, and the crushed stone drain pile 4 is formed in the liquefiable formation 5
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Construction of the crushed stone drain pile is performed as follows. First, the casing is penetrated to a predetermined location to a predetermined depth. Then, the crushed stone is charged and filled from the upper part of the casing, and then the casing is pulled up. This completes the placement of one crushed stone drain pile. Following this procedure, crushed stone drain piles will be sequentially placed.

In the present embodiment, the depth of the stratum 5 that is likely to be liquefied is 11.0 m, and a crushed stone drain pile having a diameter of 0.5 m is closely contacted with a region 6.0 m away from the steel sheet pile. 12 layers are cast.

As a result, the drainage property of the ground outside the steel sheet pile is improved, and the rise in excess pore water pressure that causes liquefaction can be suppressed, and the steel sheet pile can be held in a stable state. , It has become possible to obtain the seismic stability of the existing structure 1.

A second embodiment of the present invention is shown in FIG. (A) is a top view, (b) is sectional drawing, (c) is an enlarged view of the crushed stone drain pile part of (a). The crushed stone drain pile 4 is placed on the ground 2 of the existing structure 1 while compacting the crushed stone, and the individual crushed stone drain piles are closely attached to surround the existing structure 1 to form the wall of the crushed stone drain pile. Is forming.
The crushed stone drain pile 4 is driven only into the stratum 5 that is easily liquefied.

The crushed stone drain pile is constructed as follows. First, a placing machine is installed at a predetermined place, and a casing having a thrust rod inside is penetrated to a predetermined depth. Then, after the crushed stones are charged and filled from the upper part of the casing, the casing is pulled up while the crushed stones are tamped with a stick. At this time, if the crushed stone is compacted while measuring and controlling the reaction force applied to the thrust rod, a stable ground compaction effect can be obtained. This completes the placement of one crushed stone drain pile. The next crushed stone drain pile is placed in close contact with the crushed stone drain pile by the procedure described above. In the same manner, crushed stone drain piles will be placed one after another to complete the wall of the crushed stone drain pile.

In this embodiment, the depth of the strata 5 that is likely to be liquefied is 10.0 m, and a crushed stone drain pile having a diameter of 0.5 m is formed in 13 layers in a region up to 6.5 m away from the steel sheet pile. It is being cast. The reaction force of 1.4 Ton was applied to the cue stick. Then, when the N value indicating the degree of tightness of the ground was measured in the ground around the wall of the crushed stone drain pile, the value before the construction was 2-14, but was significantly improved to 10-22 after the construction.

As a result, the surrounding ground is compacted and the shear deformation that causes liquefaction is suppressed, and the drainage of the ground is improved, and the increase in excess pore water pressure that causes liquefaction is also suppressed. As a result, the seismic resistance of the existing structure 1 can be obtained.

[0022]

EFFECTS OF THE INVENTION Since a strength member such as a steel sheet pile is driven to surround the existing structure and a crushed stone drain pile is driven to surround the strength member, the existing structure is The ground's soil resistance to liquefaction increased, and it became possible to maintain sufficient seismic stability.

Further, the crushed stone drain piles are placed on the ground of the existing structure while compacting the crushed stones, and the individual crushed stone drain piles are closely contacted so as to surround the existing structure to form the walls of the crushed stone drain piles. Therefore, the resistance against the liquefaction of the ground of the existing structure increased, and it became possible to maintain sufficient seismic stability.

[Brief description of drawings]

1A and 1B are views showing a first embodiment of the present invention, in which FIG. 1A is a plan view, FIG. 1B is a sectional view, and FIG. 1C is an enlarged view of a crushed stone drain pile portion of FIG.

2A and 2B are views showing Embodiment 2 of the present invention, in which FIG. 2A is a plan view, FIG. 2B is a sectional view, and FIG. 2C is an enlarged view of a crushed stone drain pile portion in FIG. 2A.

FIG. 3 is a view showing a conventional steel sheet pile ring construction method,
(A) is a plan view and (b) is a sectional view.

[Explanation of symbols]

 1 ... Existing structure 2 ... Ground 3 ... Strength member 4 ... Crushed stone drain pile 5 ... Liquefaction-friendly stratum 6 ... Non-liquefaction stratum 13 ... Steel sheet pile

Claims (2)

[Claims] 1. An existing structure characterized by having a strength member driven into the ground so as to surround the existing structure and a crushed stone drain pile driven so as to surround the outside of the strength member. Ground structure. 2. The ground structure of an existing structure, comprising a wall of a crushed stone drain pile that is cast into the ground so as to surround the existing structure while compacting the crushed stone.