JP2009062709A - Wall-shaped soil improving body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively suppress or prevent liquefaction without improving soil directly below a structure. <P>SOLUTION: In this wall-shaped soil improving body 100 which is formed in the upper ground 12, the periphery of an interior wall 102 formed outside a building 10 immediately below the building is enclosed with an exterior wall 104, and an orthogonal wall 106 makes the interior and exterior walls 102 and 104 connected to each other. Thus, the out-of-plane rigidity of the wall-shaped soil improving body 100 is high. Thereby, out-of-plane-direction deformation is suppressed. This suppresses the shear strength of the upper ground which is enclosed with (the interior wall 102 of) the wall-shaped soil improving body 100 (maintains the effect of inhibiting shear deformation), and suppresses or prevents the liquefaction. In other words, the liquefaction of the upper ground 12B is inexpensively and effectively suppressed or prevented without the improvement of the upper soft ground immediately below the building 10. Consequently, damage to the building 10 by the liquefaction is suppressed or prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wall-like ground improvement body formed on a ground that may be liquefied.

  As an anti-liquefaction measure, a ground improvement method is known in which a planar grid-like wall-like ground improvement body is formed on a soft ground that may be liquefied (see, for example, Patent Document 1).

  Furthermore, in order to counter the horizontal force in the event of an earthquake, a high horizontal strength foundation method has been proposed in which a foundation pile whose lower end penetrates into a hard lower ground that does not liquefy is built in the lattice part of the wall-like ground improvement body. Yes. And a foundation slab is installed at the top of this foundation pile, and a building is built on this foundation slab. Further, the wall-like ground improvement body is configured to have a lattice portion in which a foundation pile is not constructed in a region corresponding to, for example, a stepped portion on the outside of the foundation slab (FIG. 4 of Patent Document 2). See).

  However, it is very costly to provide a planar grid-like wall-like ground improvement body on the ground immediately below an existing building and take measures against liquefaction.

  Therefore, conventionally, as a countermeasure for preventing liquefaction of the ground directly under the existing building, as shown in FIG. 5, a method of forming a cylindrical wall body 500 on the upper ground 350 so as to surround the outside directly under the building 300. Has been taken. Thereby, the liquefaction of the upper layer ground 350B is prevented or suppressed by suppressing the shear deformation of the upper layer ground 350B surrounded by the wall body 500.

  However, when the planar shape of the existing building 300 is large, the wall 500 is bent and deformed in the out-of-plane direction due to the fluid pressure of the liquefied upper ground 350A outside the wall 500. The shear deformation of the ground 350B is not sufficiently suppressed. Therefore, in order to suppress the bending deformation in the out-of-plane direction, a method of increasing the wall thickness and increasing the out-of-plane rigidity like the wall body 600 shown in FIG. 6 can be considered, but the cost increases.

Therefore, by providing a retaining wall perpendicular to the outer surface (projecting outward from the outer surface) at a predetermined interval on the outer surface of the continuous surrounding wall (wall body) constructed around the foundation structure of the building, A configuration that suppresses bending deformation and suppresses shear deformation of the ground in the surrounding wall has been proposed (see, for example, FIG. 2 of Patent Document 3).
JP 61-5114 A Japanese Patent No. 2645899 Japanese Patent Laid-Open No. 10-18308

  Now, since the retaining wall of FIG. 2 of patent document 3 is in contact with the liquefied ground outside the surrounding wall, the frictional force is small. Therefore, the effect which suppresses the bending deformation of the surrounding wall by the fluid pressure of the liquefied ground is small. For this reason, the effect which suppresses the shear deformation of the ground in a surrounding wall, ie, a structure just under a structure, is small.

  The present invention has been made to solve the above problems, and an object thereof is to effectively suppress or prevent liquefaction without improving the ground directly under the structure.

  The wall-like ground improvement body according to claim 1 is a wall-like ground improvement body formed on a ground that may be liquefied, and surrounds the outside directly below the structure provided on the ground. It is characterized by comprising an inner wall formed, an outer wall that is formed outside the inner wall with a space therebetween and that surrounds the inner wall, and an orthogonal wall that is orthogonal to the inner wall and the outer wall.

  The wall-like ground improvement body according to claim 1 has a configuration in which the outer wall surrounds the inner wall and the orthogonal wall is orthogonal to the inner wall and the outer wall, so that the out-of-plane rigidity is high. Therefore, the deformation | transformation of the out-of-plane direction by the fluid pressure of the liquefied ground outside a wall-shaped ground improvement body is suppressed.

  In addition, since the liquefaction of the ground around the orthogonal wall (between the outer wall and the inner wall) is prevented or suppressed, the frictional force between the orthogonal wall and the ground is large. Therefore, the effect of increasing the out-of-plane rigidity and suppressing the bending deformation in the out-of-plane direction of the wall-shaped ground improvement body (inner wall) is great.

  Therefore, even if the ground outside the wall-shaped ground improvement body liquefies due to an earthquake or the like, the shear deformation of the ground surrounded by the wall-shaped ground improvement body (inner wall) is suppressed (the effect of inhibiting shear deformation is maintained). Therefore, liquefaction of the ground surrounded by the wall-like ground improvement body (inner wall), that is, the ground directly under the structure is suppressed or prevented.

  That is, liquefaction is effectively suppressed or prevented without improving the ground directly under the structure. As a result, damage due to liquefaction is suppressed or prevented.

  The wall-like ground improvement body according to claim 2 is characterized in that, in the configuration according to claim 1, an intermediate wall perpendicular to the orthogonal wall is formed between the inner wall and the outer wall. Yes.

  In the wall-shaped ground improvement body according to claim 2, since the intermediate wall orthogonal to the orthogonal wall is formed between the inner wall and the outer wall, the out-of-plane rigidity is further increased. Therefore, even if the ground outside the wall-shaped ground improvement body liquefies due to an earthquake or the like, the shear deformation of the ground surrounded by the wall-shaped ground improvement body (inner wall) is suppressed (the shear deformation inhibiting effect is more reliable). Maintained). Therefore, liquefaction is more effectively suppressed or prevented without improving the ground directly under the structure.

  As described above, according to the wall-like ground improvement body according to claim 1, an excellent effect that liquefaction can be effectively suppressed or prevented without improving the ground directly under the structure. Have

  According to the wall-like ground improvement body of Claim 2, it has the outstanding effect that liquefaction can be suppressed or prevented more effectively.

  Hereinafter, an example of the embodiment of the wall-like ground improvement body in the present invention will be described with reference to FIGS. FIG. 1 is a partial cross-sectional perspective view showing ground improvement using the wall-like structure 100 (a part of the building 10 is indicated by an imaginary line). 2A is a plan view, and FIG. 2B is a cross-sectional view taken along the line AA in FIG. In FIG. 2B, only the wall-like improvement body 100 is hatched. FIG. 3 is a perspective view showing a wall-like ground improvement body 100 used for ground improvement.

  As shown in FIGS. 1 and 2, a building 10 is built on a soft upper ground 12 that may be liquefied. As shown in FIG. 2B, the building 10 is supported by a foundation 24 and a pile 22. In addition, the lower end 22A of the pile 22 is penetrated into the hard lower ground 14 which is not likely to be liquefied, below the upper ground 12. Moreover, each side of the outer periphery of the building 10 is set to 30 m to 50 m.

  As shown in FIGS. 1 and 2, a wall-like ground improvement body 100 is formed on the outer side of the upper ground 12 immediately below the building 10 to improve the ground. The wall-shaped ground improvement body 100 is made into the cylinder shape which reaches the upper end part 12H from the lower end part 12L of the upper layer ground 12 (refer also FIG. 3).

  As shown in FIGS. 1 to 3, the wall-like ground improvement body 100 includes an inner wall 102 that is formed so as to surround the outer side immediately below the building 10, and an inner wall 102 that is formed with an interval on the outer side of the inner wall 102. A surrounding outer wall 104. An orthogonal wall 106 orthogonal to the inner wall 102 and the outer wall 104 connects the inner wall 102 and the outer wall 104.

  In other words, the wall-shaped ground improvement body 100 has an upper layer so that a cylindrical tube portion 110 having a rectangular horizontal cross section surrounded by the inner wall 102, the outer wall 104, and the orthogonal wall 106 surrounds the outside directly below the building 10. It is configured to reach the upper end 12H from the lower end 12L of the ground 12.

  In addition, the wall-like ground improvement body 100 is formed by stirring and mixing the slurry formed by mixing a stabilizer or the like with a stabilizer and water at an appropriate ratio in an upper layer using a deep layer processor. (Deep Cement Mixing method).

  Next, the operation of this embodiment will be described.

  The wall-like ground improvement body 100 formed on the upper ground 12 has a configuration in which an outer wall 104 surrounds an inner wall 102 formed immediately outside the building 10, and an orthogonal wall 106 connects the inner wall 102 and the outer wall 104. Therefore, the out-of-plane rigidity is high.

  Since the upper ground 12C (see FIG. 2B) around the orthogonal wall 106 (between the inner wall 102 and the outer wall 104) is prevented or suppressed, the friction between the orthogonal wall 106 and the upper ground 12C. Power is great. Therefore, the out-of-plane rigidity of the wall-like ground improvement body 100 due to the friction between the orthogonal wall 106 and the upper layer ground 12C is further increased (the effect of suppressing the out-of-plane direction is great).

  Therefore, as shown in FIG. 2B, the upper ground 12A (free ground) outside the wall-like ground improvement body 100 (outside the outer wall 104) is liquefied, and the fluid pressure (arrow R) is the wall-like ground improvement body. Even if it acts on the outer wall 104 of 100 in the out-of-plane direction, the deformation in the out-of-plane direction of the wall-shaped ground improvement body 100 is suppressed.

  Thereby, the shear deformation of the upper layer ground 12B surrounded by the wall-shaped ground improvement body 100 (the inner wall 102 thereof) is suppressed (shear deformation suppression effect is maintained), and liquefaction is suppressed or prevented. That is, the liquefaction (shear failure) of the upper ground 12B can be effectively suppressed or prevented at low cost without improving the soft upper ground 12B directly under the building 10. As a result, damage to the building 10 due to liquefaction is suppressed or prevented. Moreover, the damage of the pile 22 by liquefaction is also prevented.

  In addition, since the liquefaction of the upper ground 12B can be suppressed or prevented without improving the soft upper ground 12B directly under the building 10 as described above, even if the building 10 is existing, There is no need to re-install. That is, it is possible to take measures against liquefaction of the upper ground 12B directly under the building 10 without incurring a great cost.

  Next, the results of equivalent line analysis using a two-dimensional FEM model in which the effect of preventing liquefaction of the present invention has been confirmed will be described.

  As shown in FIG. 4, the ground improvement analysis model for confirming the effect of preventing liquefaction according to the present invention has a side of a building 300 of 30 m × 30 m, and the depth of a soft upper ground 350 that may be liquefied. The length is 20 m. Similar to the wall-shaped improvement body 100 of the above-described embodiment, the wall-shaped ground improvement body 700 includes an inner wall 702, an outer wall 704, and an orthogonal wall 706, and has a cylindrical shape that reaches the upper end from the lower end portion of the upper layer ground 350. It is said that. The wall thickness t3 of the inner wall 702, the outer wall 704, and the orthogonal wall 706 of the wall-like ground improvement body 700 are all 1 m, the distance between the inner wall 702 and the outer wall 704, and the distance between the orthogonal walls 706 is 6 m (cylinder). One side of the hole 710 is 6 m).

  Further, a comparative model 1 (FIG. 5) for ground improvement using a cylindrical wall body 500 (corresponding to an inner wall) to which the present invention is not applied (not having an outer wall and an orthogonal wall), and a cylindrical wall body The same analysis was performed for comparative model 2 of ground improvement using 600 (corresponding to the inner wall). The wall 500 of the comparative model 1 in FIG. 5 has a wall thickness t1 of 1 m, and the wall 600 of the comparative model 2 has a wall thickness t2 of 3 m.

  In addition, the normal liquefaction prevention effect is confirmed by the FL value (resistivity against liquefaction) obtained from the ratio between the shear stress generated during the earthquake and the separately obtained liquefaction strength. Calculate. However, in this analysis, since the liquefaction strength is the same (constant) in all models, the difference in the effect of each model can be grasped by comparing the maximum shear stress during an earthquake. Therefore, in this FEM analysis, the maximum shear stress at the time of earthquake of the upper ground 350B immediately below the center of the building 300 in each model (inside of the wall-like ground improvement body 700 (inner wall 702) and walls 500 and 600, respectively) The maximum shear stress at the time of earthquake of the upper ground 350A (free ground) outside the wall-shaped ground improvement body 700 (outer wall 704) and the wall bodies 500 and 600 was obtained and compared.

  And this analysis result is shown in each graph (depth distribution of the maximum shear stress at the time of an earthquake) of (a)-(c) of FIG. The analysis result of the comparative model 1 shown in FIG. 5 is the graph of (a), and the analysis result of the comparative model 2 shown in FIG. 6 is the graph of (b), and the analysis model shown in FIG. The analysis result is a graph of (c). The analysis result of the wall-like ground improvement body 700 (outer wall 704), the upper ground 350A outside the wall bodies 500 and 600, and the ground below it is indicated by “free ground: ●” The analysis results of the upper ground 350B and the lower ground of the ground-like ground improvement body 700 (inside the inner wall 702) and the walls 500, 600) are indicated by “directly below the center of the building: ▲”.

[Graph (a) showing analysis result of comparative model 1]
The maximum shear stress of the upper ground 350B (depth 20m or more) just below the center of the building is lower than the maximum shear stress of the upper ground 350A (depth 20m or more) of the free ground (outside the wall 500). However, the difference is small. That is, the comparative model 1 shows that the effect of preventing liquefaction is small.

[Graph of (b) showing analysis result of comparative model 2]
The maximum shear stress of the upper ground 350B (depth 20 m or more) directly below the center of the building (inside the wall 600) is greater than the maximum shear stress of the upper ground 350A (depth 20 m or more) of the free ground (outside the wall 600). It is falling. That is, the comparative model 2 indicates that the wall body 600 has a large wall thickness and high out-of-plane rigidity, so that the effect of preventing liquefaction is large.

[Graph (c) showing analysis result of analysis model to which the present invention is applied]
The maximum shear stress at a depth of 10 m to 20 m in the upper ground 350B immediately below the center of the building (inside the wall-like ground improvement body 700 (inner wall 702)) is outside the free ground (outer wall 704 of the wall-like ground improvement body 700). It can be seen that it is much lower than the maximum shear stress of the upper ground 350A and is close to the analysis result of the comparative model 2. That is, although the wall thickness of the wall-like ground improvement body 700 (FIG. 4) is the same wall thickness 1 m as the comparative model 1, the liquefaction prevention effect substantially equivalent to the wall body 600 (FIG. 6) with a wall thickness of 3 m is obtained. It is shown that.

  Thus, the wall-like ground improvement body to which this invention was applied can obtain the liquefaction prevention effect substantially equivalent to the wall body which thickened wall thickness. That is, liquefaction measures can be taken at low cost.

  The present invention is not limited to the above embodiment.

  For example, the wall-like ground improvement bodies 100 and 700 of the above-described embodiment and analysis model have a configuration including the inner walls 102 and 702 and the outer walls 104 and 704 (see FIGS. 1 to 4), but are not limited thereto. .

  For example, when the building is large (for example, when it exceeds 50 m), the wall-shaped ground improvement body surrounding the outside directly under the building also becomes large. Therefore, in order to increase the out-of-plane rigidity, the inner wall 802 is orthogonal to the orthogonal wall 806 between the inner wall 802 and the outer wall 804 as in the wall-shaped ground improvement body 800 of the first modification shown in FIG. It is good also as a structure provided with the intermediate wall 810 surrounding. Furthermore, although illustration is abbreviate | omitted, the structure provided with two or more intermediate walls may be sufficient.

  In addition, for example, when the aspect ratio of the planar shape of the building is large, an intermediate wall is not provided on the short side portion having a high out-of-plane rigidity like the wall-like ground improvement body 900 of the second modification shown in FIG. Intermediate walls 910A and 910B may be formed between the outer wall 902A and the inner wall 904A of the long side portion with low out-of-plane rigidity, and between the outer wall 902B and the inner wall 904B, respectively.

  Further, for example, in the above-described embodiment and analysis model, the outer shape of the wall-like ground improvement body is a rectangle or a square, but is not limited thereto. It can be arbitrarily determined according to the shape of the building. For example, it may be L-shaped as schematically shown in FIG. 10A, or may be T-shaped as schematically shown in FIG.

  Further, for example, in the above embodiment, as shown in FIGS. 2B and 3, the wall-like ground improvement body 100 has an upper end portion 12 </ b> H to a lower end portion 12 </ b> L of the soft upper ground layer 12 that may be liquefied. However, the present invention is not limited to this. For example, the lower end of the wall-shaped ground improvement body 100 may be lower than the lower end portion 12L of the upper layer ground 12. Alternatively, the upper end of the wall-like ground improvement body 100 may be lower than the upper end portion 12H of the upper layer ground 12.

It is a fragmentary sectional perspective view which shows the ground improvement using the wall-shaped structure of embodiment of this invention. The ground improvement using the wall-shaped structure of embodiment of this invention is shown, (A) is a top view, (B) is a figure of AA cross section of (A). It is a perspective view which shows the wall-shaped ground improvement body of embodiment of this invention. The analysis model for confirming the liquefaction prevention effect of this invention is shown, (A) is a top view, (B) is a figure of the AA cross section of (A). The comparative model 1 which does not apply this invention is shown, (A) is a top view, (B) is a figure of the AA cross section of (A). The comparative model 2 which does not apply this invention is shown, (A) is a top view, (B) is a figure of the AA cross section of (A). (A) which shows the depth distribution of the maximum shear stress at the time of an earthquake is a graph which shows the analysis result of the comparison model 1, (b) is a graph which shows the analysis result of the comparison model 2, (c) is a graph of an analysis model. It is a graph which shows an analysis result. It is a top view which shows the wall-shaped ground improvement body of a 1st modification. It is a top view which shows the wall-shaped ground improvement body of a 2nd modification. The other shape of a wall-shaped ground improvement body is shown typically, (A) is a top view which shows a 1st example, (B) is a top view which shows a 2nd example.

Explanation of symbols

10 Building (structure)
12 Upper ground (ground that may liquefy)
12L Lower end portion 12H Upper end portion 100 Wall-like ground improvement body 102 Inner wall 104 Outer wall 106 Orthogonal wall 800 Wall-like ground improvement body 802 Inner wall 804 Outer wall 806 Orthogonal wall 810 Intermediate wall 900 Wall-like ground improvement body 902 Inner wall 904 Outer wall 906 Orthogonal wall 910A Intermediate Wall 910B Middle wall

Claims (2)

A wall-like ground improvement body formed on the ground that may be liquefied,
An inner wall formed so as to surround the outside directly under the structure provided on the ground;
An outer wall formed on the outer side of the inner wall with a space therebetween,
An orthogonal wall orthogonal to the inner wall and the outer wall;
A wall-like ground improvement body characterized by comprising.   The wall-shaped ground improvement body according to claim 1, wherein an intermediate wall orthogonal to the orthogonal wall is formed between the inner wall and the outer wall.

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