JP4189078B2 - Construction method of underground structure in liquefied ground - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for constructing an underground structure in a ground that may be liquefied, and a foundation structure.
[0002]
[Prior art]
In the ground that may be liquefied, that is, the ground that contains a lot of sand, shirasu, etc., high pressure is generated in the pore water due to the vibration and impact at the time of the earthquake, and the effective stress of the ground decreases accordingly and liquefies. The liquefied earth and sand vibrate in a predetermined direction, and hydrodynamic pressure acts on the underground structure. For such hydrodynamic pressure, it is proposed to improve the ground below the underground structure by, for example, compaction method or consolidation method, or to form a pile foundation on the ground below the underground structure. ing.
[0003]
Here, the compacting method is a method of constructing sandy pillars by pressing coarse sand or the like into the ground improvement place and compacting the surrounding ground of the sandy pillars. In addition, the consolidation method includes a deep mixing method and a cement injection method, in which a stabilizer such as liquid cement is pressed into the ground improvement site and mixed with a stirring blade to form a pile having strength, Cement is injected to solidify the ground.
[0004]
[Problems to be solved by the invention]
Although the above conventional compaction method needs to improve the ground not only under the underground structure but also over a wide range within the main collapse angle, it may not be possible to improve the ground over a wide range depending on the construction environment. . Moreover, the conventional caking method needs to form a large improved body in order to stabilize the improved body, and requires several times the construction cost as compared with the compacting method. Furthermore, in order to improve the horizontal bearing strength in conventional pile foundations, it is necessary to drive high-diameter, high-rigidity piles at a high density, which is several times more expensive than the compaction method. It takes.
[0005]
The present invention focuses on the drawbacks of the prior art described above, and is intended to solve this problem. The problem is that the hydraulic fluid by liquefaction can be improved by simply improving the ground directly under the underground structure by a compacting method with a low construction cost. An object of the present invention is to provide a foundation structure and a construction method for an underground structure that can resist pressure.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is a method for constructing an underground structure in a ground that may be liquefied, and is below a predetermined depth of the ground in the bottom plate range of the underground structure to be constructed a step of ground improvement the section up to at least the upper surface of the non-liquefied layer compacting, the steel Yamadome wall to penetrate into the non-liquid layer on both sides face to face of the bottom plate range after the soil improvement process sheet piles, forming a steel pipe sheet piles or lightweight steel sheet piles, a step of excavating the Yamadome walls to ground improved, the side walls on the improved ground is by contact with the fixing member to Yamadome wall A method for constructing an underground structure including the step of constructing the underground structure to be fixed.
[0007]
In the underground structure construction method of the present invention, the ground compaction process is the same as the conventional compaction method, and a sand-like column is constructed by pressing coarse sand or the like into the ground improvement location. This is a method of compacting the ground around the column.
[0009]
On the improved ground, a leveling material such as concrete or mortar may be laid to flatten the surface irregularities, and the underground structure may be placed on the leveling material.
[0010]
【Example】
Hereinafter, although an example is described based on an accompanying drawing, the present invention is not limited to this. FIG. 1 is a cross-sectional view showing an embodiment of a foundation structure 10 in a liquefied ground 30. The mountain retaining walls 11 a and 11 b placed on both sides of the improved ground 14, the concrete layer 13 spread on the improved ground 14 between the mountain retaining walls 11 a and 11 b, and the concrete layer 13 It includes a pit or culvert 12 as a built underground structure.
[0011]
Here, the culvert 12 is used for an electric cave for passing an electric cable or the like, an intake / discharge channel of a power plant, a road or the like. Therefore, the foundation structure 10 is extended over a predetermined distance with a predetermined width. To do. The culvert 12 is formed such that at least the lower ends of both side walls 12a and 12b, preferably the entire length in the vertical direction, abuts against the mountain retaining walls 11a and 11b. As shown in FIG. This reinforces fixing with the mountain retaining walls 11a and 11b. Further, the improved ground 14 is formed by pressing sand into the ground improvement range (improvement width W, improvement depth H) to construct a sand column 14a, and compacting the surrounding ground of the sand column 14a. Is. Further, the mountain retaining walls 11 a and 11 b have lower ends 11 a ′ and 11 b ′ embedded in the non-liquefaction layer 15, and at least the upper ends are extended to a height at which they abut against the side walls 12 a and 12 b of the culvert 12.
[0012]
FIG. 3 is a conceptual diagram simply showing the deformation that occurs in the retaining walls 11a and 11b when the ground outside the retaining walls 11a and 11b is liquefied and dynamic fluid pressures 21a and 21b are generated in the same direction. It is. Here, when receiving the hydraulic fluid pressure 21 a, the mountain retaining wall 11 a bends in the direction of arrow R as indicated by the dotted line 20 a and transmits the compressive force to the improved ground 14. On the other hand, when the mountain retaining wall 11b receives the hydrodynamic pressure 21b, the upper part of the culvert 12 bends in the direction of arrow R and the lower part of the mountain retaining wall 20b bends in the direction of arrow L as shown by the dotted line 20b. A compressive force is transmitted to the ground 14. In other words, since the mountain retaining walls 11a and 11b are arranged and fixed so as to contact the culvert 12, the culvert 12 and the mountain retaining walls 11a and 11b exhibit deformation characteristics as an integrated structure, No tensile force acts on the lower ground of 12 and only compressive force acts. Therefore, even if the ground improvement of this part is simple by the compaction method, and even if the retaining wall is a simple one formed by connecting, for example, a single steel sheet pile, these compaction Due to the interaction between the improved ground 14 and the mountain retaining walls 11a and 11b, it becomes possible to counteract the dynamic fluid pressures 21a and 21b during liquefaction.
[0013]
Next, the construction method of the underground structure in the liquefied ground will be described. First, the ground from the upper surface of the non-liquefied layer 15 to the height H is compacted and improved to form the improved ground 14. This ground improvement is performed by a conventional method using a plurality of sand columns 14a, and the improvement width W is determined in accordance with the width of the bottom slab 12c of the culvert 12 as an underground structure to be constructed. Next, the retaining walls 11a and 11b are constructed on both sides of the improved width W until they penetrate into the non-liquefied layer 15, and abdomen or a beam (not shown) is provided between the retaining walls 11a and 11b. Excavating until the improved ground 14 is reached. After excavating to a predetermined depth, concrete is laid flat on the bottom surface of the excavation and the concrete layer 13 is formed. And if the concrete layer 13 hardens | cures, the culvert 12 will be constructed | assembled between the mountain retaining walls 11a and 11b. A fixing tool 17 such as a diver is fixed in advance on the surfaces of the mountain retaining walls 11a and 11b, and the culvert 12 is formed so as to be embedded in the side walls 12a and 12b.
[0014]
【The invention's effect】
In the present invention, the underground structure and the mountain retaining wall are in contact with each other and integrated, and the ground directly under the underground structure is surrounded by the mountain retaining wall from both sides. Even if the pressure is applied, the tensile force does not act on the part surrounded by the mountain retaining wall directly under the underground structure, but only the compressive stress acts. It is possible to construct a foundation with sufficient resistance even if it is formed by the simple construction method described above and surrounded by a relatively lightweight mountain retaining wall.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a basic structure of the invention.
2 is a cross-sectional view showing a partially enlarged view of the basic structure of FIG. 1;
FIG. 3 is a diagram simply showing a deformation state of a sheet pile in the basic structure of FIG. 1;
[Explanation of symbols]
11a, 11b Mountain retaining wall 12 Calvert (underground structure)
12c Bottom plate 14 Improved ground 15 Non-liquefied layer W Bottom plate range

Claims (1)

  A method of constructing an underground structure on the ground that may be liquefied, and tightening a section from a predetermined depth of the ground to at least the upper surface of the lower non-liquefied layer in the bottom plate range of the underground structure to be constructed. A step of solidifying and improving the ground, and a step of forming a retaining wall from a steel sheet pile, a steel pipe sheet pile or a lightweight steel sheet pile until it penetrates into the non-liquefied layer on the opposite side surfaces of the bottom plate range after the ground improvement step. Excavating between the retaining walls to an improved ground; and constructing an underground structure so that both side walls abut against the retaining walls and are fixed by a fixing tool on the improved ground; Of building underground structures including

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