JP3797926B2 - Ground improvement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In particular, the present invention relates to a ground improvement method for the purpose of preventing liquefaction and fluidization of the lower ground and surrounding ground of an existing structure.
[0002]
[Prior art]
In general, in soft sand ground, when sand saturated with water is severely repeatedly sheared during an earthquake, the pore water pressure rises rapidly, causing the liquefaction phenomenon that the liquid loses its shear resistance and becomes liquid. It is known that this liquefaction phenomenon will cause enormous damage such as subsidence and tilting of structures on the ground.
[0003]
As such liquefaction prevention measures, so far, (1) a method of solidifying the entire ground by injecting solidifying material such as soil cement or chemicals to increase the ground strength against liquefaction, (2) a structure built on the ground A method of constructing a continuous rectangular or grid-like underground wall around the object or directly below the ground to suppress the shear deformation of the ground and block the movement of groundwater and liquefied soil, (3) In the ground A method of disposing the drainage material to dissipate the water pressure generated during liquefaction, (4) a method of increasing the effective stress of the ground by lowering the groundwater level, and (5) a lot of sand piles etc. in the ground A method of increasing the density of the surrounding ground by placing is known.
[0004]
[Problems to be solved by the invention]
However, all of these countermeasures have problems such as large-scale construction, high construction costs, and inevitable extension of the construction period.
[0005]
For example, as a method of solidifying the entire ground by injecting a solidifying material, for example, a temporary trench is excavated around a structure built on the ground, and a drilling hole is drilled horizontally in the ground directly under the structure in the trench. However, a method of injecting solidified material into the ground from this borehole is known, but not only does it require tremendous cost and labor to excavate trenches, but it is also necessary to improve the ground over a wide area. There is a problem that the construction cost is considerably increased because it is consumed in large quantities, and further, the excavation of the trench and the work in the trench have a problem in the safety of the work due to the collapse of the natural ground.
[0006]
On the other hand, as a method for constructing the underground continuous wall in the ground, for example, a method of constructing the underground continuous wall around the structure or in the ground directly below by driving a number of steel sheet piles into the ground is known. However, there is a problem that it is very difficult to completely close the ground because the pipes buried in the ground get in the way.
[0007]
Furthermore, since the underground continuous wall acts as a bending material against seismic force and lateral flow during liquefaction, the underground continuous wall can be made considerably thicker to resist large earth pressure. However, it is necessary to form a dense lattice or to have a high-strength wall, and there is a problem that the construction cost is considerably increased.
[0008]
The present invention has been made to solve the above problems, and in particular, provides a ground improvement method capable of suppressing liquefaction, fluidization, and subsidence / dissimilar subsidence of existing structures around and immediately under existing structures. For the purpose.
[0009]
[Means for Solving the Problems]
The ground improvement construction method according to claim 1 is characterized in that the improved underground wall is formed in the vertical direction so as to surround the ground around the structure and directly below the ground.
[0010]
In this case, the improved underground wall may be formed along the outer periphery of the structure, or may be formed to have a small diameter and scattered throughout the ground at predetermined intervals. Moreover, you may form an improved underground wall in double.
Here, the improved underground wall is an underground wall improved and created in a spiral shape, and may be separated from each other, or may have a small separation width to form one wall body.
[0011]
The ground improvement method according to claim 2 is characterized in that, in the ground improvement method according to claim 1, the improved underground wall is continuously formed in the vertical direction.
[0012]
The ground improvement construction method according to claim 3 is the ground improvement construction method according to claim 1 or 2, wherein the improved underground wall is formed along the outer periphery of the structure. For example, when a structure built on the ground has a flat circular shape, the improved underground wall is formed into a flat circular shape, and when the ground structure has a flat rectangular shape, the improved underground wall is formed into a flat rectangular shape. do it.
[0013]
The ground improvement construction method according to claim 4 is the ground improvement construction method according to claim 1, 2 or 3, wherein an underground pile is formed outside the improved underground wall along the outer periphery of the structure. It is. In this case, the underground pile is constructed to reinforce the improved underground wall from the outside, and may be, for example, an RC pile, a PC pile, a steel pile, or the like.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1A and 1B show an example of a ground improvement method according to the present invention. In the figure, a cylindrical structure (for example, a large cylindrical storage tank) is placed on a sand ground 1 that may be liquefied. Etc.) 2 is constructed, and an improved underground wall 3 is formed in the sand ground 1 immediately below the structure 2.
[0015]
The improved underground wall 3 is continuously formed in a planar circular spiral from the ground surface to the hard ground 4 immediately below the sand ground 1 along the outer periphery of the structure 2, and the improved underground wall 3 is located in the continuous direction. A certain amount of prestress has been introduced.
[0016]
In addition , underground piles 5 are installed outside the improved underground wall 3 along the outer periphery of the structure 2 at predetermined intervals. And the upper end and lower end of the improved underground wall 3 and the intermediate part are also restrained by the underground pile 5 as needed. As the underground pile 5 in this case, RC pile, PC pile, steel pile, etc. are constructed.
[0017]
Since the improved underground wall 3 as described above is formed in the sand ground 1 immediately below the structure 2, the pore water pressure around the structure 2 and the immediate ground is rapidly increased during the earthquake, and the sand ground 1 becomes liquid. However, even if the structure immediately below and surrounding ground becomes likely to flow to the side, the sand ground 1 directly below structure 2 is surrounded by an improved diaphragm wall 3, moreover a predetermined amount to the continuous direction improved diaphragm wall 3 The prestress is introduced, and the underground pile 5 is constructed outside the improved underground wall 3, so that the liquefaction of the sand ground 1 directly under the structure 2 and the side of the sand ground 1 at the time of liquefaction It is possible to prevent side flow and shear deformation at the time of an earthquake, thereby suppressing the settlement and non-uniform settlement of the structure 2 built on the ground.
[0018]
As a construction method of the improved underground wall 3, for example, a PC steel wire 3b is inserted as a tension material into a perforated tube or a mesh-like tube 3a, and this is inserted into the sand ground 1 along the outer shape of the structure 2 from the ground surface. There is a method of inserting a solid circular material 3c, such as cement, into the tube 3a from the ground at a high pressure by inserting the hard ground 4 directly under the sand ground 1 into a flat circular spiral shape.
[0019]
By constructing in this way, the solidified material 3c injected into the tube 3a flows out into the surrounding sand ground 1 from the hole or mesh on the surface of the tube 3a, and solidifies together with the surrounding sand to improve the predetermined diameter. The inner wall 3 can be formed.
[0020]
In addition, by fixing the tip of the PC steel wire 3b in the hard ground 4 and tensioning the PC steel wire 3b before the solidified material 3c is solidified, a predetermined amount of prestress is applied to the improved underground wall 3 in its continuous direction. Can be introduced.
[0021]
The improved underground wall 3 can be formed into an arbitrary cross-sectional shape by appropriately selecting the cross-sectional shape of the tube 3a. For example, to make the improved underground wall 3 a rectangular cross-sectional shape, the cross-section of the tube 3a The shape may be a vertically long rectangular cross section.
[0022]
Moreover, the pitch P between the improved underground walls 3 and 3 can be freely set according to the ground condition of the sand ground 1, and a plurality of PC steel wires 3b may be arranged.
[0023]
【The invention's effect】
The present invention is as described above, and by forming an improved underground wall that spirals in the vertical direction in the periphery of the structure and in the ground directly below, the gap between the periphery of the existing structure and the immediate foundation ground during an earthquake. Even if the water pressure rises and the sand ground liquefies and tries to flow to the side, it can be reliably prevented by the improved underground wall that spirals continuously, liquefaction of the sand ground directly under the structure, In addition, it is possible to prevent lateral flow of the sand ground during liquefaction and shear deformation during an earthquake, thereby suppressing subsidence and non-uniform subsidence of structures built on the ground.
[Brief description of the drawings]
FIG. 1 shows an example of a ground improvement method according to the present invention, wherein (a) is a perspective view thereof, and (b) is an enlarged view of a portion in (a).
[Explanation of symbols]
1 Sand ground 2 Structure (eg large cylindrical storage tank)
3 improved underground wall 3a tube 3b PC steel wire 3c solidified material 4 hard ground 5 underground pile

Claims (4)

A ground improvement method characterized by forming an improved underground wall spirally in the vertical direction so as to surround the ground around and around the structure. 2. The ground improvement method according to claim 1, wherein the improved underground wall is formed continuously in the vertical direction. The ground improvement method according to claim 1 or 2, wherein the improved underground wall is formed along the outer periphery of the structure. The ground improvement construction method according to claim 1, 2, or 3, wherein an underground pile is formed outside the underground improvement wall along the outer periphery of the structure .

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