JP2007046343A - Liquefaction preventive construction method of ground just under existing building - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a construction method of preventing liquefaction of the ground just under an existing building. <P>SOLUTION: An earth retaining wall reaching up to the depth of a low water permeable layer is constructed around the existing building. An underground water level is lowered by pumping, and a work area is formed by excavating up to the depth of exposing a stratum having a risk of liquefying the surrounding ground of the existing building. An adit is formed by excavating the exposed stratum having risk of liquefaction in a tunnel shape from the work area, and a ground improvement wall is formed by being hardened by filling a mixture of a cement-based solidifying agent and excavation earth in the adit. An end part of the ground improvement wall is also integrated with the earth retaining wall, and hereafter, the formation of the adit and the formation of the ground improvement wall are advanced in the stratum having a risk of liquefaction so that the ground improvement wall is arranged in a grating shape. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention belongs to the technical field of a construction method for preventing liquefaction of a direct foundation board of an existing building, and more specifically, a liquid layer to be applied to a stratum that is deposited relatively thinly on a direct foundation board of an existing building and has a risk of liquefaction. It relates to anti-oxidation method.

  For example, the following techniques (i) and (ii) are well known as liquefaction prevention methods that can be suitably applied to a formation that may be liquefied and deposited on a direct foundation board of an existing building.

(I) The liquefaction prevention method disclosed in Patent Document 1 is to make a hole in the foundation slab of an existing building, and use this hole to form a conical ground improvement body in a stratum that may liquefy directly under the foundation slab. is doing.

(Ii) The liquefaction prevention method described in Patent Documents 2 and 3 boils the ground diagonally so that it reaches the liquefied stratum deposited on the immediate foundation board of the existing building from the surface area around the existing building. The stratum that may liquefy when it reaches is drilled horizontally, and a ground improvement body is formed around the horizontal borehole.

(Iii) By the way, the liquefaction prevention method of Patent Documents 4 and 5 is not applied to a liquefied formation layer deposited on the direct foundation of an existing building, but the ground improvement walls are formed in a grid-like arrangement. is doing.
JP 2001-164549 A JP 2001-207437 A Japanese Patent No. 2920802 JP-A-1-290817 Japanese Examined Patent Publication No. 4-54004

  Since the liquefaction prevention method of the above-mentioned Patent Document 1 is constructed by opening a hole in the foundation slab of an existing building, it is necessary to remove the installation on the foundation slab. Therefore, there is a problem that construction cannot be performed while using an existing building.

  The liquefaction prevention method of Patent Documents 2 and 3 boils the ground diagonally so as to reach the formation that may be liquefied from the surface portion around the existing building and accumulated on the direct foundation plate of the existing building. The start position of the boring is a position away from the existing building. Therefore, there is a problem that construction cannot be performed unless there is sufficient space around the existing building.

  The liquefaction prevention methods described in Patent Documents 4 and 5 are not techniques for constructing a liquefied ground layer deposited on a direct foundation board of an existing building, but differ in technical fields.

  Accordingly, an object of the present invention is to provide a method for preventing liquefaction of a direct foundation board of an existing building that can be constructed while using the existing building and can be constructed even if there is not enough space around the existing building. .

As a means for solving the above-mentioned problems of the prior art, the liquefaction prevention method for the direct foundation board of the existing building according to the invention described in claim 1 is:
It is a liquefaction prevention method that is applied to a stratum that has a risk of liquefaction deposited relatively thinly on the direct foundation board of an existing building,
Build a retaining wall that reaches the depth of the low-permeability layer around the existing building, lower the groundwater level by pumping, and work by excavating to a depth that exposes a layer that may liquefy the surrounding ground of the existing building A horizontal tunnel is formed by excavating the exposed liquefied formation in a tunnel shape from the work area to form a horizontal shaft, and the horizontal shaft is filled with a mixture of cement-based solidifying agent and excavated soil. The ground improvement wall cured and formed, and further, the end of the ground improvement wall is extended to be integrated with the retaining wall, and the ground improvement wall may be liquefied so that the ground improvement wall has a lattice arrangement. It is characterized by the formation of a horizontal pit and a ground improvement wall in a certain formation.

The invention according to claim 2 is a method for preventing liquefaction of a direct foundation panel of an existing building according to claim 1,
A first step of constructing a retaining wall that reaches the depth of the low permeability layer around the existing building, and lowering the groundwater level by pumping;
In the surrounding ground of the existing building, a work area is formed by excavating the position facing the existing building across the existing building to a depth at which the formation that may be liquefied is exposed, and the liquefaction exposed from the work area A ground improvement wall in which a horizontal shaft is formed by excavating a stratum that may be damaged to a height that reaches the bottom of an existing building, and a horizontal solid shaft is filled with a mixture of cement-based solidifying agent and excavated soil. A second step of extending the end of the ground improvement wall and integrating it with the mountain retaining wall to refill the work area,
Hereinafter, the formation of the ground improvement wall is promoted by repeating the second step so that the ground improvement wall has a lattice arrangement.

The invention according to claim 3 is the liquefaction prevention method for the direct foundation panel of the existing building according to claim 1,
A first step of constructing a retaining wall that reaches the depth of the low permeability layer around the existing building, and lowering the groundwater level by pumping;
In the surrounding ground of the existing building, a work area is formed by excavating the position facing the existing building across the existing building to a depth at which the formation that may be liquefied is exposed, and the liquefaction exposed from the work area A ground improvement wall in which a horizontal shaft is formed by excavating a stratum that may be damaged to a height that reaches the bottom of an existing building, and a horizontal solid shaft is filled with a mixture of cement-based solidifying agent and excavated soil. Forming a second step to refill the work area;
Hereinafter, the second step is repeated to advance the formation of the ground improvement wall so that the ground improvement wall has a lattice arrangement, and the edge of the ground improvement wall is used from the outer periphery of the existing building using the ground improvement device. The part is extended and integrated with the retaining wall.

Invention of Claim 4 is the liquefaction prevention construction method of the direct foundation board of the existing building described in Claim 1,
A retaining wall that reaches the depth of the low-permeability layer is built around the existing building, the groundwater level is lowered by pumping, and the entire surrounding ground of the existing building is excavated to a depth that exposes the liquefied layer. A first step of forming a work area;
From the working area, the exposed liquefied formation is tunneled to a height reaching the bottom of the existing building to form a horizontal shaft, and a mixture of cement-based solidifying agent and excavated soil is formed in the horizontal shaft Forming a ground improvement wall filled and hardened, extending the end of the ground improvement wall and integrating with the retaining wall;
Hereinafter, the second step is repeated to advance the formation of the ground improvement wall so that the ground improvement wall has a lattice arrangement, and the work area is finally backfilled.

Invention of Claim 5 is in the liquefaction prevention construction method of the direct foundation board of the existing building described in Claim 1,
A retaining wall that reaches the depth of the low-permeability layer is built around the existing building, the groundwater level is lowered by pumping, and the entire surrounding ground of the existing building is excavated to a depth that exposes the liquefied layer. A first step of forming a work area;
From the working area, the exposed liquefied formation is tunneled to a height reaching the bottom of the existing building to form a horizontal shaft, and a mixture of cement-based solidifying agent and excavated soil is formed in the horizontal shaft A second step of forming a ground improvement wall filled and hardened,
Hereinafter, the second step is repeated to advance the formation of the ground improvement wall so that the ground improvement wall has a grid-like arrangement, finally the work area is backfilled, and the ground improvement is further performed from the outer periphery of the existing building. Using the apparatus, the end of the ground improvement wall is extended and integrated with the retaining wall.

Invention of Claim 6 is the liquefaction prevention construction method of the direct foundation board of the existing building as described in any one of Claims 1-5,
When excavating a stratum that may be liquefied in a tunnel shape, the excavation proceeds while the ground including the excavated slope is reinforced with a mixture of a cement-based solidifying agent and excavated soil.

The liquefaction prevention method of the direct foundation board of the existing building according to the invention described in claim 7 is:
It is a liquefaction prevention method that is applied to a stratum that is deposited relatively thinly on an immediate foundation board of an existing building and that may be liquefied.
Build a retaining wall that reaches the depth of the low-permeability layer around the existing building, lower the groundwater level by pumping, and work by excavating to a depth that exposes a layer that may liquefy the surrounding ground of the existing building A horizontal tunnel is formed by excavating the exposed liquefied formation in a tunnel shape from the work area to form a horizontal shaft, and the horizontal shaft is filled with a mixture of cement-based solidifying agent and excavated soil. Forming a ground improvement wall that has been hardened, and then proceeding with the formation of a horizontal shaft and the formation of a ground improvement wall in the formation that may be liquefied so that the ground improvement wall has a lattice arrangement. And

  The method for preventing liquefaction of the direct foundation board of an existing building according to the present invention is to construct a retaining wall around the existing building, lower the groundwater level by pumping, and excavate the surrounding ground of the existing building to form a work area. Then, the ground improvement walls are formed in a grid-like arrangement in the stratum that may be liquefied from the work area directly under the exposed existing building. Further, the end of the ground improvement wall is extended from the work area or from the outer periphery of the existing building to be integrated with the retaining wall. In short, construction can proceed from the outside of the existing building and it will not affect the existing building at all.

  In addition, the area of the work area only needs to be large enough to allow excavation work of a formation that may cause a worker to liquefy from the work area. Therefore, it can be constructed even if there is not enough space around the existing building, and can be suitably constructed for a stratum that may be liquefied directly under an existing building with a small site area such as an urban area.

  By the way, if the non-liquefied layer deposited just below the layer that may liquefy is a solid layer that can support the existing building sufficiently, the grid-like ground improvement wall should be in contact with the bottom of the existing building. It becomes possible to transmit the load of the existing building to the non-liquefaction layer through the ground improvement wall. Therefore, even if an earthquake that exceeds the expected level occurs and the inside of the grid-like ground improvement wall is liquefied, and the bearing capacity of the stratum that may be liquefied is lost, settlement of the existing building can be prevented and liquefaction can be prevented. This will improve the earthquake performance of existing buildings, including strata that may be damaged.

  Build a retaining wall that reaches the depth of the low-permeability layer around the existing building, lower the groundwater level by pumping, and work by excavating to a depth that exposes a layer that may liquefy the surrounding ground of the existing building Form a region. A ground formed by excavating the exposed liquefied formation from the working area in a tunnel shape to form a horizontal shaft, and filling the horizontal shaft with a mixture of a cement-based solidifying agent and excavated soil and hardening the ground. Form an improved wall. Further, both ends of the ground improvement wall are extended to be integrated with the retaining wall, and the formation of horizontal shafts and ground improvement walls are formed in the formation where there is a risk of liquefaction so that the ground improvement walls are arranged in a lattice form. Promote the formation of

  Embodiments of a liquefaction prevention method (hereinafter abbreviated as a liquefaction prevention method) for a direct foundation board of an existing building according to the invention described in claims 1, 2 and 6 will be described with reference to the drawings. The liquefaction prevention method of the present invention is suitably applied to the formation 2a that is deposited relatively shallowly (that is, about 2 m to 3 m to the extent that humans can dig) and is likely to liquefy. .

  First, a mountain retaining wall 3 (a typical soil cement column wall or the like is adopted) reaching the depth of the low water permeability layer 2b around the existing building 1 (see FIGS. 1A and 1B). .

  A plurality of (six in this embodiment) deep wells 4 are installed so as to reach the depth of the non-liquefied layer 2c deposited immediately below the formation 2a that may be liquefied. The groundwater continues to be pumped from the deep well 4 so that the groundwater level Δh becomes lower than the formation 2a that may be liquefied (see FIGS. 2A and 2B). Then, a work area 6 for forming a horizontal shaft 5 (see FIG. 3 (B)) penetrating in the X-axis direction through a substantially central portion of the formation 2a that may be liquefied is set in advance. In order to form at both ends of the excavation position of the mine 5, there is a risk that the position of the existing ground 1 around the existing building 1 that lies in the X-axis direction across the existing building 1 may be liquefied with a predetermined width. Excavation to a depth H where the formation 2a is exposed. By the way, the area of the work area 6 may be an area capable of satisfactorily excavating the formation 2a from which the worker may liquefy.

  A tunnel-shaped horizontal shaft 5 is formed from the working area 6 in the exposed formation 2a that may be liquefied (see FIGS. 3A and 3B). Specifically, the load on the existing building 1 is transferred from one work area 6 to the surrounding work area 6 so as to penetrate through the substantially central portion of the formation 2a that may be liquefied to the other work area 6. While being supported by the ground 2, the formation 2 a that may be liquefied is dug up to a height that reaches the bottom surface 1 a of the existing building 1 (that is, over almost the entire height) with a predetermined width dimension T. At this time, the surrounding ground (that is, the surrounding ground of the horizontal shaft 5) 5a including the excavated slope is reinforced with the soil cement 8 (however, any member that can reinforce the peripheral ground 5a of the horizontal shaft 5 is used). When the digging is continued, the surrounding ground 5a of the horizontal pit 5 does not collapse and is safe (the invention according to claim 6). In addition, although the width dimension T of the horizontal shaft 5 is set in consideration of the load of the existing building 1 to be supported and the supporting force of the formation 2a that may be liquefied, it is about 1 m as an example.

  The openings on both sides of the horizontal shaft 5 are closed with a mold (not shown), and the concrete filling hole previously formed in one mold is filled with soil cement (however, a chemical solution used for usual ground improvement) A mixture of excavated soil may be used.) 9 is filled and hardened to form the ground improvement wall 10a in the X-axis direction. Further, in order to integrate the ground improvement wall 10a and the retaining wall 3, a work frame 6, 6 is assembled with a formwork (not shown), filled with soil cement 9, and hardened to extend both ends of the ground improvement wall 10a. Then, it is integrated with the retaining wall 3 and the work areas 6 and 6 are backfilled (see FIGS. 4A and 4B).

  Next, it is confirmed that the soil cement 9 of the ground improvement wall 10a in the X-axis direction is hardened and develops strength, and the ground improvement wall 10b in the Y-axis direction is formed.

  First, work areas 12 for forming the horizontal shafts 11 and 11 that are substantially perpendicular to the ground improvement wall 10a in the X-axis direction so as to be horizontally opposed to both sides of the ground improvement wall 10a In order to form at the outer end portion of the excavation position of 11 and 11, there is a risk of liquefying at a predetermined area in the peripheral ground 7 of the existing building 1 with a predetermined width in the Y-axis direction relative to the existing building 1 The excavation is carried out to a depth at which the stratum 2a with a certain depth is exposed. Incidentally, the area of the work area 12 may be any area as long as the excavation work of the formation 2a in which the worker may be liquefied later from the work area 12 can be satisfactorily performed in the same manner as the work area 6.

  Tunnel-like horizontal shafts 11 and 11 are formed in the exposed formation layer 2a from the work areas 12 and 12 which may be liquefied. Specifically, the workers reach the bottom surface 1a of the existing building 1 from the respective work areas 12 and 12 so that the worker can hit the ground improvement wall 10a in the X-axis direction substantially perpendicularly to the ground improvement wall 10a. Digging to a height with a predetermined width dimension. At this time, since the surrounding ground 5a of the ground improvement wall 10a (horizontal pit 5) in the X-axis direction is reinforced by the soil cement 8, the soil cement 8 is torn down so as to abut against the ground improvement wall 10a in the X-axis direction. A horizontal shaft 11 is formed. Therefore, the soil cement 8 that reinforces the surrounding ground 5a of the ground improvement wall 10a is a soil cement having a relatively low strength. The horizontal wells 11 and 11 are filled with soil cement 9 to form a ground improvement wall 10b in the Y-axis direction. Further, in order to integrate the ground improvement wall 10b and the retaining wall 3, a work frame 12, 12 is assembled with a mold (not shown), filled with soil cement 9, and hardened to extend the end of the ground improvement wall 10b. Then, it is integrated with the mountain retaining wall 3, and the work areas 12 and 12 are refilled (see FIG. 5).

  Hereinafter, the surrounding ground 7 of the existing building 1 is excavated so as to form a new ground improvement wall 10b in the Y-axis direction by opening a predetermined distance N (see FIG. 6) from the ground improvement wall 10b in the Y-axis direction. Then, the work area 12 is formed, and the formation 2a formed by excavating the liquefied formation 2a exposed from the work area 12 is formed, and the side pit 11 is filled with the soil cement 9 and cured. The process of forming the ground improvement wall 10b and extending the end of the ground improvement wall 10b and integrating it with the retaining wall 3 is repeated (the remaining one in this embodiment), and the ground integrated with the retaining wall 3 is repeated. The improved walls 10a and 10b are formed in a lattice arrangement. The mutual distance N between the ground improvement walls 10b and 10b in the Y-axis direction varies depending on the assumed magnitude of ground motion and ground conditions. For example, Japanese Patent Application Laid-Open No. 2001-355229 (Liquid in a grid improvement ground by a deep mixing treatment method) It is better to set according to the lattice spacing simple calculation method for prevention of stabilization.

  Finally, when the deep well 4 is removed, the construction of the liquefaction prevention method is completed (see FIG. 6, inventions of claims 1 and 2).

  The above-described liquefaction prevention method is a structure in which the retaining wall 3 is constructed around the existing building 1 and the exposed formation layer from the work area 6 formed by excavating the surrounding ground 7 of the existing building 1 is exposed. 2 a is excavated to form a horizontal shaft 5, filled with soil cement 9 in the horizontal shaft 5 and hardened to form a ground improvement wall 10 a in the X-axis direction, and both ends of the ground improvement wall 10 a are extended. And integrated with the retaining wall 3. Hereinafter, the exposed formation layer 2a which may be liquefied from the work area 12 formed by excavating the surrounding ground 7 of the existing building 1 so as to be in a grid arrangement with the ground improvement wall 10a in the X-axis direction. Excavation forms a horizontal pit 11, fills the horizontal pit 11 with soil cement 9 and hardens it to form a ground improvement wall 10 b in the Y-axis direction, and further extends the end of the ground improvement wall 10 b to fix it The process of integrating with the wall 3 is repeated. In short, since construction is carried out from the outside of the existing building 1 and the existing building 1 is not affected at all, it can be constructed while using the existing building 1.

  In addition, the area of the work area 6 (12) may be an area that can satisfactorily perform excavation work of the formation 2a from which the worker may be liquefied from the work area 6 (12). Therefore, it can be constructed even if there is not enough space around the existing building 1, and it can be suitably constructed for the stratum 2 a that may be liquefied directly under the existing building 1 with a small site area such as an urban area.

  In particular, the liquefaction prevention method of the present embodiment only excavates the surrounding ground 7 of the existing building 1 partially when forming the ground improvement wall 10a (10b). Even if an earthquake occurs during construction, it is safe.

  By the way, when the non-liquefied layer 2c deposited immediately below the formation 2a that may be liquefied is a solid formation that can sufficiently support the existing building 1, the grid-like ground improvement walls 10a and 10b are connected to the existing building. By being formed so as to be in contact with the bottom surface 1a, the load of the existing building 1 can be transmitted to the non-liquefied layer 2c through the ground improvement walls 10a and 10b. Therefore, even if an earthquake more than expected occurs and the inside of the grid-like ground improvement walls 10a and 10b is liquefied, the settlement of the existing building 1 is prevented even if the supporting force of the formation 2a that may be liquefied is lost. Thus, the performance of the existing building 1 including the geological formation 2a that may be liquefied is improved.

  In the liquefaction prevention method of Example 1 described above, the work area 6 (12) was formed every time the ground improvement wall 10a (10b) was formed. However, the work area 13 was excavated all at once around the surrounding ground 7 of the existing building 1. May be formed. The liquefaction prevention method according to the present embodiment is suitably implemented when the existing building 1 has a large plane area and the formation 2a that may be liquefied exhibits a large supporting force. Since this liquefaction prevention method is substantially the same as the liquefaction prevention method of Example 1, only the different parts will be briefly described.

  Specifically, the work area 13 is formed by excavating the entire area around the ground 7 of the existing building 1 to a depth at which the formation 2a that may be liquefied is exposed (see FIG. 7).

  Excavating the formation 2a that may be liquefied from the work area 13 to form a horizontal shaft 5, filling the horizontal shaft 5 with soil cement 9 and curing it to form a ground improvement wall 10a in the X-axis direction, Further, both ends of the ground improvement wall 10a are extended and integrated with the retaining wall 3 (see FIG. 8).

  After confirming that the soil cement 9 of the ground improvement wall 10a in the X-axis direction is hardened and develops strength, the work area 13 butts substantially perpendicular to the ground improvement wall 10a in the X-axis direction. Then, excavating the formation 2a that may be liquefied to form the horizontal shafts 11, 11, and filling the horizontal shafts 11, 11 with the soil cement 9 to harden to form the ground improvement wall 10b in the Y-axis direction, Further, the end of the ground improvement wall 10b is extended and integrated with the retaining wall 3 (see FIG. 9).

  Hereinafter, in order to form a new ground improvement wall 10b in the Y-axis direction at a predetermined interval from the ground improvement wall 10b in the Y-axis direction, the above-described step of forming the ground improvement wall 10b is repeated (this embodiment) In the remaining one), the ground improvement walls 10a and 10b integrated with the retaining wall 3 are formed in a lattice arrangement.

  Finally, when the work area 13 is backfilled and the deep well 4 is removed, the construction of the liquefaction prevention method is completed (incorporation of FIG. 6, invention of claim 4).

  In the liquefaction prevention methods of Examples 1 and 2, the work area 6 (12, 13) is backfilled after the end of the ground improvement wall 10a (10b) is extended and integrated with the retaining wall 3. After the work area 6 (12, 13) is backfilled, the end of the ground improvement wall 10a (10b) is extended from the outer periphery of the existing building 1 by using a ground improvement device (not shown), and the retaining wall 3 (Inventions according to claims 3 and 5).

  In the liquefaction prevention methods of the first and second embodiments, the ground improvement wall 10b in the Y-axis direction is formed after the ground improvement wall 10a in the X-axis direction is formed. In the range that can be supported by, it may be formed simultaneously.

  In the liquefaction prevention method of the first and second embodiments, the soil cement 9 is filled in the horizontal shafts 5 and 11 at once, but may be divided and filled depending on the length of the horizontal shafts 5 and 11. .

  In the liquefaction prevention method of Examples 1 and 2 described above, only one ground improvement wall 10a in the X-axis direction was formed. It may be formed (see FIG. 10). In this case, the portion that intersects the ground improvement wall 10b in the Y-axis direction is filled with a soil cement 14 having a relatively low strength, the portion filled with the soil cement 14 is demolished, and the horizontal shaft 11 is formed. A ground improvement wall 10b in the Y-axis direction may be formed in the horizontal shaft 11.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and can be implemented in various forms without departing from the gist of the present invention. In short, the ground improvement walls 10a and 10b are formed in a lattice shape from the work area 6 (12, 13) formed by excavating the surrounding ground 7 of the existing building 1 to the formation 2a exposed by the excavation work and which may be liquefied. What is necessary is just to form in arrangement | positioning and to integrate with the retaining wall 3, and the timing and the area which excavate the surrounding ground 7, and the magnitude | size, space | interval, shape, etc. of the ground improvement walls 10a and 10b are not specifically limited. Further, even if the ground improvement walls 10a and 10b are not integrated with the retaining wall 3, it is not particularly necessary to integrate them if shearing force due to an earthquake or the like can be mutually transmitted (invention of claim 7).

A is the longitudinal cross-sectional view which showed the step which built the retaining wall around the existing building in the liquefaction prevention construction method of the direct foundation board of the existing building of Example 1. FIG. B is a horizontal sectional view of A. FIG. A is the longitudinal cross-sectional view which showed the step which excavated the surrounding ground of the existing building in the liquefaction prevention construction method of the direct foundation board of the existing building of Example 1. FIG. B is a horizontal sectional view of A. FIG. A is the longitudinal cross-sectional view which showed the step which formed the horizontal pit in the stratum which has the possibility of liquefying under the existing building in the liquefaction prevention construction method of the direct foundation board of the existing building of Example 1. FIG. B is a horizontal sectional view of A. FIG. A is a longitudinal cross-sectional view showing a stage in which a ground improvement wall in the X-axis direction is formed in a stratum that may be liquefied directly under an existing building in the liquefaction prevention method for a direct foundation board of an existing building of Example 1. FIG. . B is a horizontal sectional view of A. FIG. It is the horizontal sectional view which showed the step which formed the ground improvement wall of the Y-axis direction in the stratum which has a possibility of becoming liquefaction just under the existing building in the liquefaction prevention construction method of the direct foundation board of the existing building of Example 1. It is the horizontal sectional view which showed the step which the construction of the liquefaction prevention construction method of the direct foundation board of the existing building of Example 1 was completed. It is the horizontal sectional view which showed the stage which excavated the surrounding ground of the existing building in the liquefaction prevention construction method of the direct foundation board of the existing building of Example 2. FIG. It is the horizontal sectional view which showed the stage which formed the ground improvement wall of the X-axis direction in the stratum which has a possibility of liquefaction just under the existing building in the liquefaction prevention construction method of the direct foundation board of the existing building of Example 2. It is the horizontal sectional view which showed the step which formed the ground improvement wall of the Y-axis direction in the stratum which may be liquefied just under the existing building in the liquefaction prevention construction method of the direct foundation board of the existing building of Example 2. In the method for preventing liquefaction of the immediate foundation board of the existing building of Example 6, a plurality of ground improvement walls in the X-axis direction are formed in the formation that may be liquefied immediately under the existing building, and the ground improvement wall and the Y-axis direction are formed. It is the horizontal sectional view which showed the step which forms the ground improvement wall of this by a grid | lattice-like arrangement | positioning.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Existing building 2 Direct foundation board of existing building 2a Ground layer which may be liquefied 3 Mountain retaining wall 4 Deep well 5 Horizontal shaft 6 Working area 8 Soil cement 9 Soil cement 10a Ground improvement wall 10b Ground improvement wall 11 Horizontal shaft 12 Working area 13 Work area

Claims (7)

It is a liquefaction prevention method that is applied to a stratum that has a risk of liquefaction deposited relatively thinly on the direct foundation board of an existing building,
Build a retaining wall that reaches the depth of the low-permeability layer around the existing building, lower the groundwater level by pumping, and work by excavating to a depth that exposes a layer that may liquefy the surrounding ground of the existing building A horizontal tunnel is formed by excavating the exposed liquefied formation in a tunnel shape from the work area to form a horizontal shaft, and the horizontal shaft is filled with a mixture of cement-based solidifying agent and excavated soil. The ground improvement wall cured and formed, and further, the end of the ground improvement wall is extended to be integrated with the retaining wall, and the ground improvement wall may be liquefied so that the ground improvement wall has a lattice arrangement. A method for preventing the liquefaction of a direct foundation board of an existing building, characterized by promoting the formation of a horizontal pit and a ground improvement wall in a certain formation. A first step of constructing a retaining wall that reaches the depth of the low permeability layer around the existing building, and lowering the groundwater level by pumping;
In the surrounding ground of the existing building, a work area is formed by excavating the position facing the existing building across the existing building to a depth at which the formation that may be liquefied is exposed, and the liquefaction exposed from the work area A ground improvement wall in which a horizontal shaft is formed by excavating a stratum that may be damaged to a height that reaches the bottom of an existing building, and a horizontal solid shaft is filled with a mixture of cement-based solidifying agent and excavated soil. A second step of extending the end of the ground improvement wall and integrating it with the mountain retaining wall to refill the work area,
2. The liquid of the direct foundation board of an existing building according to claim 1, wherein the ground improvement wall is formed by repeating the second step so that the ground improvement wall has a lattice arrangement. Prevention method. A first step of constructing a retaining wall that reaches the depth of the low permeability layer around the existing building, and lowering the groundwater level by pumping;
In the surrounding ground of the existing building, a work area is formed by excavating the position facing the existing building across the existing building to a depth at which the formation that may be liquefied is exposed, and the liquefaction exposed from the work area A ground improvement wall in which a horizontal shaft is formed by excavating a stratum that may be damaged to a height that reaches the bottom of an existing building, and a horizontal solid shaft is filled with a mixture of cement-based solidifying agent and excavated soil. Forming a second step to refill the work area;
Hereinafter, the second step is repeated to advance the formation of the ground improvement wall so that the ground improvement wall has a lattice arrangement, and the edge of the ground improvement wall is used from the outer periphery of the existing building using the ground improvement device. The method for preventing liquefaction of a direct foundation board of an existing building according to claim 1, wherein the part is extended and integrated with the retaining wall. A retaining wall that reaches the depth of the low-permeability layer is built around the existing building, the groundwater level is lowered by pumping, and the entire surrounding ground of the existing building is excavated to a depth that exposes the liquefied layer. A first step of forming a work area;
From the working area, the exposed liquefied formation is tunneled to a height reaching the bottom of the existing building to form a horizontal shaft, and a mixture of cement-based solidifying agent and excavated soil is formed in the horizontal shaft Forming a ground improvement wall filled and hardened, extending the end of the ground improvement wall and integrating with the retaining wall;
In the following, the second step is repeated to advance the formation of the ground improvement wall so that the ground improvement wall has a grid-like arrangement, and the work area is finally backfilled. The liquefaction prevention method for the direct foundation board of the existing building described. A retaining wall that reaches the depth of the low-permeability layer is built around the existing building, the groundwater level is lowered by pumping, and the entire surrounding ground of the existing building is excavated to a depth that exposes the liquefied layer. A first step of forming a work area;
From the working area, the exposed liquefied formation is tunneled to a height reaching the bottom of the existing building to form a horizontal shaft, and a mixture of cement-based solidifying agent and excavated soil is formed in the horizontal shaft A second step of forming a ground improvement wall filled and hardened,
Hereinafter, the second step is repeated to advance the formation of the ground improvement wall so that the ground improvement wall has a grid-like arrangement, finally the work area is backfilled, and the ground improvement is further performed from the outer periphery of the existing building. The method for preventing liquefaction of a direct foundation board of an existing building according to claim 1, wherein an end of the ground improvement wall is extended using a device to be integrated with the retaining wall.   2. When excavating a stratum that may be liquefied in a tunnel shape, excavation proceeds while the ground including the excavated slope is reinforced with a mixture of a cement-based solidifying agent and excavated soil. The liquefaction prevention construction method of the direct foundation board of the existing building described in any one of -5. It is a liquefaction prevention method that is applied to a stratum that is deposited relatively thinly on an immediate foundation board of an existing building and that may be liquefied.
Build a retaining wall that reaches the depth of the low-permeability layer around the existing building, lower the groundwater level by pumping, and work by excavating to a depth that exposes a layer that may liquefy the surrounding ground of the existing building A horizontal tunnel is formed by excavating the exposed liquefied formation in a tunnel shape from the work area to form a horizontal shaft, and the horizontal shaft is filled with a mixture of cement-based solidifying agent and excavated soil. Forming a ground improvement wall that has been hardened, and then proceeding with the formation of a horizontal shaft and the formation of a ground improvement wall in the formation that may be liquefied so that the ground improvement wall has a lattice arrangement. The liquefaction prevention method for the direct foundation board of existing buildings.

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