Ground improvement foundation structure and method for constructing the same

Abstract

To provide a ground improvement foundation structure and a method for constructing the same, which can support a surface improvement ground part solidified and improved in ground surface by a columnar improvement part and disperse a building load within the wide range of a lower compaction target layer of the columnar improvement part.SOLUTION: This ground improvement foundation structure comprises: a surface improvement ground part 3 solidified and improved in ground surface within a range wider than the outer periphery of a foundation part 2 which receives a building load; and a columnar improvement part 4 provided with a plurality of columnar bodies 41 within the ground of the range wider than the outer periphery of the foundation part 2 and supporting the surface improvement ground part 3 by the columnar bodies 41.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ground improvement foundation structure that enables a building to be constructed on soft ground, and a method for constructing a ground improvement foundation structure. [Background technology]

[0002] Patent Document 1 discloses a foundation construction method in which the ground is improved, then the improved soil is excavated, and a concrete pouring section is formed using the excavated surface of the improved soil as a formwork, reinforcing bars are placed in the concrete pouring section, and then concrete is poured into the concrete pouring section.

[0003] Patent Document 2 discloses a foundation structure for a building constructed on soft ground that is designed to correct the inclination of a building when uneven settlement occurs in the building constructed on top of soft ground, the foundation structure comprising a base layer provided on the surface layer of the foundation ground for the building, a plurality of support piles provided in the foundation ground to support the central part of the base layer, and a slab foundation placed on top of the base layer, the central part of the base layer supported by the support piles being one step higher, on which the central part of the slab foundation is placed, and adjustment sand is filled in the gap between the base layer and the slab foundation around the central part. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-299387 A [Patent Document 2] Patent No. 4773797 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the structure disclosed in Patent Document 1 is not a structure in which the surface improved panel section, which has been solidified and improved, is supported by the columnar improvement section. On the other hand, the panel structure disclosed in Patent Document 2 is a structure in which the surface improved panel section, which has been solidified and improved, is supported by the columnar improvement section, but it is not capable of distributing the building load over a wide area of ​​the consolidation target layer below the columnar improvement section.

[0006] In view of the above circumstances, an object of the present invention is to provide a ground improvement foundation structure and a method for constructing a ground improvement foundation structure that can support a surface improvement panel section, which has solidified and improved the surface layer of the ground, with a columnar improvement section, and can distribute the building load over a wide area of ​​the consolidation target layer below the columnar improvement section. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the ground improvement foundation structure of the present invention is characterized in having a surface improvement board section in which the surface layer of the ground is solidified and improved over an area wider than the periphery of the foundation section that bears the building load, and a columnar improvement section in which a plurality of columnar bodies are provided in the ground over an area wider than the periphery of the foundation section, and in which the columnar bodies support the surface improvement board section.

[0008] With the above-mentioned ground improvement foundation structure, the foundation section that receives the building load is supported by the surface improvement board section that is located in an area wider than the outer periphery of the foundation section, and the columnar improvement section that supports this surface improvement board section is constructed in an area wider than directly below the foundation section, so that the building load can be distributed over a wide area of ​​the consolidation target layer below the columnar improvement section, thereby further suppressing consolidation settlement.

[0009] The columnar body located on the outermost side may be located within a point where an imaginary line extending outward from the outer periphery of the foundation part at an angle of 45 degrees to 60 degrees downward with respect to the horizontal direction intersects with a location on the underside of the surface improvement board part. In this way, the building load on the outer periphery side of the foundation part is supported by the columnar body located on the outermost side due to stress dispersion at the angle of 45 degrees to 60 degrees.

[0010] The surface improved section may have an inverted frustum shape, and the outer peripheral surface of the surface improved section may be inclined with respect to the vertical plane. With this, the surface improved section can be stably supported by the surrounding ground due to the inclination (wedge effect), and the building load can be distributed to the ground on the sides of the surface improved section, thereby suppressing uneven settlement.

[0011] A first floor floor slab may be constructed on the surface improvement board. In this way, the surface improvement board is provided as far as possible below the first floor floor slab, so that the soil in the construction site is used as effectively as possible for solidification and improvement, and the generation of surplus soil can be suppressed.

[0012] The ground improvement foundation structure according to the present invention is a ground improvement foundation structure having a surface-improved board section in which the surface of the ground is solidified and improved over an area wider than the periphery of the foundation section that bears the building load, and a columnar improvement section in which a plurality of columnar bodies are provided in the ground and support the surface-improved board section by the columnar bodies, characterized in that the outer peripheral side of the surface-improved board section has higher bending rigidity and shear rigidity than the inner side of the surface-improved board section. This makes it possible for the load at the outer peripheral position of the foundation section of a replacement building to be received by the outer peripheral side of the surface-improved board section, which has higher bending rigidity and shear rigidity.

[0013] In addition, the construction method of the present invention is a construction method for the ground improvement foundation structure, and is characterized by including a step of constructing the surface improvement board section in which the surface layer of the ground is solidified and constructing the columnar improvement section using a plurality of columnar bodies provided in the ground, and a step of creating the foundation section within the surface improvement board section.

[0014] In the above construction method, the foundation is a slab, and the construction stage of the slab may include the steps of: excavating the surface improvement board to match the extension shape of the slab; arranging reinforcement within the construction range of the slab including the recessed portion where the excavation was performed; preparing an outer periphery formwork only at the portion corresponding to the outer periphery of the slab; and pouring ready-mixed concrete within the area surrounded by the outer periphery formwork. According to this, the outer periphery formwork is prepared only at the portion corresponding to the outer periphery of the slab, and ready-mixed concrete is poured within the area surrounded by the outer periphery formwork, thereby reducing the number of construction steps and shortening the construction period. In addition, backfilling of soil around the foundation is minimized, thereby increasing horizontal resistance during earthquakes.

[0015] The construction method of the present invention is a construction method for a ground improvement foundation structure having a surface layer improvement board section in which the surface layer of the ground is solidified and improved over an area wider than the outer periphery of the foundation section that bears the building load, and a columnar improvement section in which a plurality of columnar bodies are provided in the ground and the columnar bodies support the surface layer improvement board section, The method includes the steps of constructing the surface layer improvement section in which the surface layer of the ground is solidified and constructing the columnar improvement section using a plurality of columnar bodies provided in the ground, and creating the foundation section in the surface layer improvement section, The foundation portion is a slab footing, and the construction stage of this slab footing is characterized by including the steps of: excavating the surface improvement board portion to match the extension shape of the slab footing; placing reinforcement within the construction range of the slab footing including the recessed areas where the excavation was performed; creating an outer perimeter formwork only at the areas corresponding to the perimeter of the slab footing; and pouring ready-mixed concrete within the area surrounded by the outer perimeter formwork.

[0016] According to this construction method, an outer perimeter formwork is created only in the area corresponding to the outer perimeter of the slab footing, and ready mixed concrete is poured in the area enclosed by the outer perimeter formwork, so the number of construction steps can be reduced and the construction period can be shortened. In addition, backfilling of the soil around the foundation can be minimized, increasing horizontal resistance during earthquakes. Effect of the Invention

[0017] The present invention has various advantages, such as being able to distribute the building load over a wide area of ​​the layer to be consolidated below the columnar improvement section. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is an explanatory diagram showing a ground improvement foundation structure according to an embodiment. [Diagram 2] FIG. 11 is an explanatory diagram showing another embodiment of a ground improvement foundation structure. [Diagram 3] FIG. 11 is an explanatory diagram comparing the load acting on the consolidation target layer between a conventional configuration and an embodiment of the ground improvement foundation structure. [Figure 4] FIG. 11 is an explanatory diagram illustrating an example of replacing a building on a ground improvement foundation structure of an embodiment with a larger building. [Diagram 5] FIG. 13 is an explanatory diagram illustrating an example of a case in which a large building is constructed on a ground improvement foundation structure whose perimeter is reinforced according to an embodiment. [Figure 6] FIG. 2 is an explanatory diagram showing a method for constructing a ground improvement foundation structure according to an embodiment. [Figure 7] FIG. 7 is an explanatory diagram showing a step following the construction method shown in FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. As shown in Figures 1 and 2, a ground improvement foundation structure 1 of the embodiment has a surface layer improvement board section 3 in which the surface layer of the ground is solidified and improved over an area wider than the periphery of a foundation section 2 that bears the building load, and a columnar improvement section 4 in which a plurality of columnar bodies 41 are provided in the ground over an area wider than the periphery of the foundation section 2, and which supports the surface layer improvement board section 3 with these columnar bodies 41.

[0020] In this embodiment, the foundation portion 2 is a continuous foundation, and between the foundation beams 21 of this continuous foundation, there is a mound 31 of the surface improvement board portion 3 at a position higher than the ground level GL, and the first floor floor slab 22 is constructed in contact with the upper surface of this mound 31. The pitch of the foundation beams 21 is 2500 mm in the example shown in Fig. 1, and 3500 mm in the example shown in Fig. 2.

[0021] In the example shown in Figure 1, the distance (thickness T) between the underside of the foundation beam 21 and the underside of the surface improved board portion 3 is 1000 mm, and in the example shown in Figure 2, the thickness T of the surface improved board portion 3 is 1500 mm. Also, in the example shown in Figure 1, the outer peripheral edge position of the upper surface of the surface improved board portion 3 is located 2500 mm away from the outer peripheral position of the foundation portion 2. Also, the strength of the surface improved board portion 3 is, for example, a design ground pressure of 50 kN / m 2 150kN / m, three times the force 2 That is all.

[0022] Moreover, the surface improvement plate portion 3 has an inverted frustum shape with a lower surface area smaller than the upper surface area of ​​the surface improvement plate portion 3, and the outer peripheral surface of the surface improvement plate portion 3 is inclined inward at a predetermined angle with respect to the vertical plane. This angle of inclination is, for example, greater than 0° and not greater than 45°. Of course, the surface improvement plate portion 3 can also be in a form without such inclination (inclination angle 0°).

[0023] The columnar improvement section 4 is constructed by providing cylindrical columnar bodies 41 in a grid pattern. In the columnar improvement section 4, the center of the columnar body 41 located on the outermost side is located within the point where an imaginary line extending outward from the outer periphery of the foundation section 2 at an angle of 45 degrees to 60 degrees downward with respect to the horizontal direction intersects with a location on the underside of the surface improvement board section 3.

[0024] In this embodiment, the arrangement pitch of the columnar bodies 41 is set so that they are located at points where an imaginary line extending outward from the foundation beams 21 at an angle of 45 degrees to 60 degrees downward with respect to the horizontal direction intersects with a location on the underside of the surface improvement board section 3. For example, in the example shown in Fig. 1, the center-to-center pitch of the columnar bodies 41 is 2500 mm, and in the example shown in Fig. 2, the center-to-center pitch of the columnar bodies 41 is 3500 mm. Note that if the foundation section 2 is a slab foundation, the center-to-center pitch of the columnar bodies 41 can be made wider.

[0025] In Fig. 3, the upper part of the figure shows the distribution of load acting on the consolidation target layer in a ground improvement foundation structure having only columnar improvement parts as a conventional configuration, and the lower part of the figure shows the distribution of load acting on the consolidation target layer in the ground improvement foundation structure 1 of the embodiment. This figure was created with reference to the equivalent load surface method described in the Architectural Institute of Japan's Building Foundation Design Guidelines.

[0026] In the embodiment of the ground improvement foundation structure 1, a surface improvement board section 3 is provided in which the surface layer of the ground has been solidified and improved over an area wider than the outer periphery of the foundation section 2 which receives the building load, and the columnar improvement section 4 which supports this surface improvement board section 3 is constructed over an area wider than directly below the foundation section 2, so that, as shown in Figure 3, the building load can be distributed over a wide area of ​​the consolidation target layer below the columnar improvement section 4, further suppressing consolidation settlement due to the columnar improvement section 4. The surface improvement board section 3 also makes it possible to distribute the building load in the consolidation target layer.

[0027] In addition, a simulation result was obtained in which, when a separate building is constructed around a ground improvement foundation structure having only a columnar improvement section as the conventional configuration on the upper side in Fig. 3, large consolidation settlement occurs between this ground improvement foundation structure and the separate building, but when a separate building is constructed around the ground improvement foundation structure 1 of the embodiment, a simulation result was obtained in which consolidation settlement between this ground improvement foundation structure 1 and the separate building is small. In other words, if the building is planned to be built using the ground improvement foundation structure 1, it is possible to reduce the impact of surrounding buildings.

[0028] In addition, when the columnar body 41 located on the outermost side is located within the point where an imaginary line extending outward from the outer periphery of the foundation section 2 at an angle of 45 degrees to 60 degrees downward relative to the horizontal direction intersects with a point on the underside of the surface improvement board section 3, the building load on the outer periphery side of the foundation section 2 is supported by the columnar body 41 located on the outermost side due to stress dispersion at an angle of 45 degrees to 60 degrees.

[0029] Moreover, the surface improved board part 3 has an inverted frustum shape with a lower surface area smaller than the upper surface area of ​​the surface improved board part 3, and the outer peripheral surface of the surface improved board part 3 is inclined inward with respect to the vertical plane. As a result, the surface improved board part 3 is stably supported by the surrounding ground due to the above-mentioned inclination (wedge effect), and the building load is distributed to the ground on the sides of the surface improved board part 3, making it possible to suppress uneven settlement.

[0030] When the first floor floor slab 22 is constructed on top of and in contact with the surface improvement board section 3, the surface improvement board section 3 is provided as far as possible below the first floor floor slab 22, so that the soil within the construction site is utilized as effectively as possible for solidification and improvement, and the generation of residual soil can be suppressed.

[0031] 4 shows a case where a large foundation 2 is to be constructed when an existing building is demolished and replaced with a larger building. In this case, the outermost foundation beams 21 of the large foundation 2 may be located outside the columnar bodies 41 located on the outermost side.

[0032] Figure 5 also shows the creation of a large foundation section 2 when an existing building is demolished and replaced with a larger building, but in this example, reinforcing fibers (fiber length approximately 30 mm to 100 mm) made of resin or steel are added to the outer periphery side 33 of the surface improved board section 3 (the range including the upper part of the columnar body 41 on the outer periphery side of the columnar improvement section 4), so that the outer periphery side 33 has higher bending rigidity and shear rigidity than the inner side of the surface improved board section 3. As a result, even if the foundation section 2 of a large replacement building protrudes from the outer periphery of the columnar improvement section 4, it is possible for the outer periphery side 33 of the surface improved board section 3, which has higher bending rigidity and shear rigidity, to withstand the load at the outer periphery position of the foundation section 2.

[0033] Next, a method for constructing the ground improvement foundation structure 1A will be described with reference to Figures 6 and 7. The ground improvement foundation structure 1A has a surface layer improvement board section 3 in which the surface layer of the ground has been solidified and improved over an area wider than the outer periphery of the foundation section 2 that bears the building load, and a columnar improvement section 4A in which a number of columnar bodies 41 are provided in the ground over an area roughly equivalent to the outer periphery of the foundation section 2, and the columnar improvement section 4A supports the surface layer improvement board section 3 with the columnar bodies 41.

[0034] For example, as shown in (a) of Fig. 6, a plurality of pillars 41 are formed in the ground to form the pillar improvement section 4A. The pillars 41 are, for example, concrete pillars made in the ground using heavy machinery from the soil of the ground. The pillars 41 are preferably made to a length of, for example, 2 to 12 m and reach the supporting layer, but may also function as friction piles without reaching the supporting layer.

[0035] Next, as shown in (b) of Figure 6, the surface layer of the ground is solidified and improved on the columnar improvement section 4A to create the surface improvement board section 3. This surface improvement board section 3 is created, for example, by pouring a cement-based solidification material onto the soil of the ground and mixing it using a bucket such as a backhoe. The surface improvement board section 3 is created to a depth of, for example, about 2m. Note that the hardness of the surface improvement board section 3 can be increased by increasing the amount of cement-based solidification material.

[0036] The surface improvement board section 3 may be prepared prior to preparing the columnar bodies 41. In other words, after making sure that the heavy machinery does not tilt on the surface improvement board section 3, the heavy machinery may be used to form multiple columnar bodies 41 from the top to the bottom of the surface improvement board section 3, thereby preparing a columnar improvement section 4A in which the upper sides of the columnar bodies 41 exist within the surface improvement board section 3.

[0037] Next, as shown in (c) of Figure 6, a strip footing is constructed as the foundation part 2 on the surface improved board part 3. In the construction stage of this strip footing, a backhoe or the like is used to form a recess 32 by excavating the surface improved board part 3 to match the extension shape of the strip footing (foundation part 2). Next, as shown in (d) of Figure 6, reinforcing bars 2a are placed within the construction range of the strip footing, including the recess 32 and the surface improved board part 3 surrounded by the recess 32.

[0038] Next, as shown in Fig. 7(a), an outer perimeter formwork 5 is fabricated only in the area corresponding to the outer perimeter of the slab (foundation part 2). After that, as shown in Fig. 7(b), ready-mixed concrete 2b is poured in the area surrounded by the outer perimeter formwork 5, and cured, and then, as shown in Fig. 7(c), a foundation beam 21 and a first floor floor slab 22 are simultaneously fabricated.

[0039] According to this construction method, the outer perimeter formwork 5 is fabricated only in the area corresponding to the outer perimeter of the continuous footing, which is the foundation portion 2, and ready mixed concrete 2b is poured in the area surrounded by this outer perimeter formwork 5, thereby reducing the number of construction steps and shortening the construction period. In addition, backfilling of the soil around the continuous footing can be minimized, thereby increasing horizontal resistance during earthquakes.

[0040] In the ground improvement foundation structure 1A constructed by the above method, the columnar improvement section 4A has multiple columnar bodies 41 provided in the ground over an area approximately the same as the outer periphery of the foundation section 2. However, a ground improvement foundation structure 1 in which a columnar improvement section 4 is constructed in the ground over an area wider than the outer periphery of the foundation section 2 can also be manufactured by going through steps similar to those shown in Figures 6 and 7.

[0041] Although the embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited to the illustrated embodiment. Various modifications and variations can be made to the illustrated embodiment within the same scope as the present invention or within an equivalent scope. [Explanation of symbols]

[0042] 1: Ground improvement basic structure 1A: Ground improvement basic structure 2:Foundation part 2a: Reinforced concrete 2b: Ready-mix concrete 3: Surface improved board section 4: Column improvement part 5: Periphery formwork 21: Foundation beam 31: The climax 32: Depression 33: Outer periphery 41: Column

Claims

1. a surface improvement section in which the surface layer of the ground is solidified and improved over an area wider than the outer periphery of the foundation section that bears the building load; a columnar improvement section including a plurality of columnar bodies provided in the ground in an area wider than the outer periphery of the foundation section, the columnar bodies supporting the surface improvement board section; A ground improvement foundation structure comprising:

2. In the ground improvement foundation structure described in claim 1, the columnar body located on the outermost side is located within the point where an imaginary line extending outward from the outer periphery position of the foundation part at an angle of 45 degrees to 60 degrees downward relative to the horizontal direction intersects with a point on the underside of the surface improvement board part.

3. 2. The ground improvement foundation structure according to claim 1, wherein the surface improvement board portion has an inverted frustum shape, and the outer peripheral surface of the surface improvement board portion is inclined with respect to a vertical plane.

4. 2. The ground improvement foundation structure according to claim 1, wherein a first floor slab is constructed on the surface improvement board portion.

5. A ground improvement foundation structure having a surface improvement board section in which the surface of the ground has been solidified and improved over an area wider than the outer periphery of the foundation section that bears the building load, and a columnar improvement section in which a plurality of columnar bodies are provided in the ground and support the surface improvement board section by the columnar bodies, characterized in that the outer periphery side of the surface improvement board section has higher bending rigidity and shear rigidity than the inner side of the surface improvement board section.

6. A method for constructing a ground improvement foundation structure as described in any one of claims 1 to 5, comprising the steps of constructing the surface improvement board section in which the surface layer of the ground is solidified and constructing the columnar improvement section using a plurality of columnar bodies provided in the ground, and creating the foundation section within the surface improvement board section.

7. A method for constructing a ground improvement foundation structure as described in claim 6, wherein the foundation portion is a slab footing, and the construction stage of this slab footing includes a step of excavating the surface improvement board portion to match the extension shape of the slab footing, a step of placing reinforcement within the construction range of the slab footing including the recessed areas where the excavation was performed, a step of preparing an outer perimeter formwork only at the points corresponding to the perimeter of the slab footing, and a step of pouring ready-mixed concrete within the area surrounded by the outer perimeter formwork.

8. A method for constructing a ground improvement foundation structure comprising: a surface layer improvement section in which the surface layer of the ground is solidified and improved over an area wider than the outer periphery of a foundation section that bears the load of a building; and a columnar improvement section in which a plurality of columnar bodies are provided in the ground and support the surface layer improvement section by the columnar bodies, The method includes the steps of constructing the surface layer improvement section in which the surface layer of the ground is solidified and constructing the columnar improvement section using a plurality of columnar bodies provided in the ground, and creating the foundation section in the surface layer improvement section, The foundation portion is a slab footing, and the construction stage of this slab footing includes the steps of: excavating the surface improvement board portion to match the extension shape of the slab footing; arranging reinforcement within the construction range of the slab footing including the recessed areas where the excavation was performed; creating an outer perimeter formwork only in areas corresponding to the perimeter of the slab footing; and pouring ready-mixed concrete within the area surrounded by the outer perimeter formwork.

Images