Pile foundation structure, building, construction method of pile foundation structure

Abstract

To provide a pile foundation structure using a reduced amount of concrete.SOLUTION: A pile foundation structure used as a foundation supporting a superstructure of a building comprises a steel pipe pile 20 driven into the ground 10, and an independent concrete foundation 30 buried in the ground, the independent concrete foundation 30 resting on the steel pipe pile 20 and having a bottom surface that is a horizontal plane parallel to the horizontal plane of an upper end of the steel pipe pile 20. The head of the steel pipe pile 20 is a horizontal plane, and the bottom surface of the independent concrete foundation 30 is a plane parallel to the horizontal plane. The independent concrete foundation 30 does not swallow the head of the steel pipe pile 20.SELECTED DRAWING: Figure 2(B)

Description

Technical Field

[0001] The present invention mainly relates to a pile foundation structure that supports the superstructure of a building, and also relates to a building including the pile foundation structure and a construction method of the pile foundation structure.

Background Art

[0002] In houses and other buildings, a foundation, which is also called a substructure that supports the superstructure, is indispensable. There are a shallow foundation and a pile foundation as the foundation. The shallow foundation is a structure in which a concrete foundation mainly made of concrete is arranged on the ground, and directly transmits the load from the superstructure of the building to the ground. On the other hand, the pile foundation drives a support body called a long and columnar pile into the ground, and transmits the load from the superstructure of the building to the ground through the pile. The shallow foundation and the pile foundation are selected and used depending on the properties of the ground and the weight of the superstructure of the building. The pile foundation may be used in combination with a concrete foundation similar to that used in the shallow foundation. In that case, a concrete foundation is arranged on the pile, but it is common to have the upper end portion of the pile swallowed into the concrete foundation, and doing so has been common sense in the construction industry for a long time.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, bending stress acts on the pile head, which is the upper end of the pile, for example when an earthquake occurs. This is because the pile is usually about 10 m or longer, and generally only the lower end and the pile head of the pile are fixed. When bending stress acts on the pile head, a large force acts on the concrete foundation that engulfs the pile head. Therefore, it is necessary to provide the concrete foundation with a means to counteract the force acting on it. From this perspective, it is common to add a ground beam, also made of concrete, to the concrete foundation that engulfs the pile head. However, the ground beams provided for the above purposes need to be provided in the vertical and horizontal directions with respect to the concrete foundation. However, among the ground beams constructed in the vertical and horizontal directions, although they are not originally necessary to receive the load of the superstructure, many of them are often mixed with those necessary only to compensate for the strength of the concrete foundation. This not only takes time to construct the ground beams but also inevitably increases the cost due to an increase in the amount of concrete used. Also, if the ground beam is not provided, it is possible to achieve the above purpose by increasing the concrete foundation in the vertical and horizontal directions or in thickness. However, even then, the cost increases because the amount of concrete used increases.

[0005] An object of the present invention is to provide a pile foundation structure that suppresses the amount of concrete used.

Means for Solving the Problem

[0006] The present invention for solving the above problems is as follows. The present invention is a pile foundation structure used as a foundation for supporting the superstructure of a building, comprising a steel pipe pile driven into the ground, and a concrete foundation made of concrete and buried in the ground, with a horizontal plane parallel to the horizontal end face at the upper end of the steel pipe pile and serving as the bottom surface, resting on the steel pipe pile. This pile foundation structure has the steel pipe pile and the concrete foundation as the minimum components. Using a steel pipe pile as the pile is often advantageous in terms of cost, delivery time, and ease of construction, such as being able to be constructed even in a narrow area. Steel pipe piles are usually driven into the ground in the normal way of use. The concrete foundation is placed on top of the steel pipe piles. There may be waste concrete between the concrete foundation and the steel pipe piles. The concrete foundation is made of concrete, has a horizontal plane parallel to the horizontal end face at the upper end of the steel pipe pile as its bottom surface, and is buried in the ground. The concrete foundation has a horizontal plane parallel to the horizontal end face at the upper end of the steel pipe pile as its bottom surface and is buried in the ground. That is, the concrete foundation does not engulf the pile head of the steel pipe pile. Thereby, even when an earthquake or the like occurs, for example, bending stress does not act on the concrete foundation from the steel pipe pile, so that a ground beam unnecessary for supporting the upper structure of the building can be eliminated, or the concrete foundation can be made relatively smaller than before, and thus the amount of concrete used can be reduced.

[0007] In the pile foundation structure of the present application, there are a plurality of the steel pipe piles, and the concrete foundation may be the same number of independent foundations independent of each other, each placed on top of each of the steel pipe piles. This is the case where the pile foundation structure has a structure similar to the independent foundation in the direct foundation. An independent foundation in the direct foundation is generally an independent foundation placed under a column in the upper structure of a building when viewed in plan. When the pile foundation structure according to the invention of the present application has an independent foundation, similar to the independent foundation of the direct foundation, a plurality of independent foundations independent of other foundations are arranged when viewed in plan, and steel pipe piles are driven under the plurality of independent foundations. Thereby, since the steel pipe piles can be positioned directly under each independent foundation, the load received by each independent foundation from the upper structure of the building can be reliably transmitted to the steel pipe pile located directly below it, so that the strength of the pile foundation structure can be increased. Note that the plurality of independent foundations are not necessarily located under the columns of the upper structure of the building. This is particularly relevant when the upper structure of the building adopts a wall-type structure as will be described later.

[0008] The independent foundation in the invention of the present application can be in the shape of a rectangular parallelepiped. In the direct foundation, the independent foundation often has a footing foundation or an inverted T-shaped structure called a mat foundation, that is, a footing with a predetermined thickness that is one size larger than the rectangular parallelepiped-shaped foundation is provided below the rectangular parallelepiped-shaped foundation. In the pile foundation structure with independent foundations according to the present invention, since steel pipe piles are provided directly below each independent foundation, footings are not required for the independent foundations. Thereby, in the present invention, not only can the amount of concrete required to construct the independent foundation be reduced, but also the shape of the formwork arranged prior to constructing the independent foundation can be made simple, so that the labor of the workers can be reduced.

[0009] In the pile foundation structure of the present application, there are a plurality of the steel pipe piles, and the concrete foundation may be a linear beam foundation in plan view, which is placed on at least two of the steel pipe piles. This is the case where the pile foundation structure has a structure similar to the beam foundation in the direct foundation. The beam foundation in the direct foundation is generally a linear foundation arranged directly under the columns in the upper structure of the building in plan view. The beam foundation in the direct foundation is provided linearly at positions corresponding to the four sides of the rectangle, for example, when columns of the upper structure of the building are erected at the four vertices of the rectangle in plan view. The beam foundations at positions corresponding to each side of the rectangle will support the columns at both ends thereof. When the pile foundation structure according to the present invention has a beam foundation, as in the beam foundation of the direct foundation, a plurality of linear beam foundations are arranged in plan view, and a plurality of steel pipe piles are driven under each of the plurality of beam foundations. It is also allowed for one steel pipe pile to be located under a plurality of beam foundations (one steel pipe pile is located under the intersection of the linear beam foundations). Thereby, since a plurality of steel pipe piles can be positioned directly below each beam foundation, the load received by each beam foundation from the upper structure of the building can be reliably transmitted to the steel pipe piles located directly below it, so that the strength of the pile foundation structure can be increased. By adopting a beam foundation in combination with steel pipe piles, the amount of concrete used and the amount of steel bars used when applicable can be reduced, and the construction period can be shortened. Note that a plurality of beam foundations are not necessarily located under the columns of the upper structure of the building. This is particularly relevant when the upper structure of the building adopts a wall-type structure as described later.

[0010] The beam foundation may be in a rectangular parallelepiped shape. When adopting a beam foundation in a rectangular parallelepiped shape, the formwork can be made into a simple shape. Therefore, compared with the case of providing a footing as described later in particular, the number of panels for constructing the formwork can be reduced, and the amount of concrete and steel bars used when applicable can be reduced, making it possible to shorten the construction period. The beam foundation in a direct foundation is usually a footing foundation or an inverted T-shaped structure called a raft foundation, that is, in many cases, a footing with a predetermined thickness projecting in the width direction from the beam foundation is provided below the width direction of a long rectangular parallelepiped-shaped foundation. In the pile foundation structure with independent foundations in the present invention, since a plurality of steel pipe piles are provided directly below each beam foundation, it is not necessary to provide a footing for the beam foundation. Thereby, in the present invention, not only can the amount of concrete required to construct the independent foundation be reduced, but also the shape of the formwork arranged prior to constructing the independent foundation can be made simple, so that the labor of the workers can be reduced. On the other hand, the beam foundation of the pile foundation structure in the present invention may be a raft foundation with a substantially T-shaped cross-section by providing a footing with a predetermined thickness at its lower end, which has a predetermined thickness and is wider than the beam foundation. According to this, it becomes possible to increase the contact area of the foundation by the amount of the footing, and due to the existence of the bearing capacity of the contact surface, it becomes possible to reduce the number of steel pipe piles or reduce the diameter of the steel pipe piles, so that it becomes possible to suppress the cost related to the steel pipe piles.

[0011] The steel pipe piles are plural, and the concrete foundation may be a bottom foundation that has a planar spread and is integrally formed in a plate shape and is placed on all of the steel pipe piles. This is the case where the pile foundation structure has a structure similar to the solid foundation in the direct foundation. The solid foundation in the direct foundation is generally a planar or plate-shaped foundation that is arranged under all the columns in the superstructure of the building when viewed in plan. The solid foundation in the direct foundation supports the columns respectively at the portions of its upper surface that are in contact with the columns. When the pile foundation structure according to the present invention has a bottom foundation, a bottom foundation that has a planar spread and is integrally formed in a plate shape is arranged in the same manner as the solid foundation of the direct foundation, and a plurality of steel pipe piles are driven under one bottom foundation. As a result, it becomes possible to position a plurality of steel pipe piles directly under the bottom foundation, so that the load received by the bottom foundation from the superstructure of the building can be reliably transmitted to the steel pipe piles located directly below it, and thus the strength of the pile foundation structure can be increased. According to this, it becomes possible to further increase the grounding area of the foundation compared to the case of the beam foundation with a footing, and it becomes possible to suppress the cost of the piles due to the presence of the bearing capacity of the grounding surface. Further, in the case of the bottom foundation, the formwork is only required at the outer peripheral portion of the bottom foundation, so the formwork can be installed easily and quickly. Note that the steel pipe piles are not necessarily located under the columns of the superstructure of the building. This is particularly relevant when the superstructure of the building adopts a wall structure as will be described later.

[0012] In the pile foundation structure according to the present invention, a reinforcing structure that contributes to the transmission of the axial force from the superstructure of the building through the steel pipe pile to the ground may be provided at the upper end of the steel pipe pile or in a predetermined range from the upper end. In the pile foundation structure according to the present invention, the load of the superstructure of the building is received by the steel pipe piles via the concrete foundation. To increase the efficiency, it is necessary to efficiently transmit the upward axial force (the reaction force of the load transmitted from the superstructure of the building to the steel pipe pile) transmitted from the steel pipe pile to the concrete foundation. If a reinforcing structure that contributes to the transmission of axial force from the upper structure of the building through the steel pipe pile to the ground is provided at the upper end of the steel pipe pile or within a predetermined range from the upper end, the axial force can be efficiently transmitted from the steel pipe pile to the concrete foundation.

[0013] To efficiently transmit the axial force from the steel pipe pile to the concrete foundation, it is advisable to increase the contact area between the steel pipe pile and the concrete foundation (and between the steel pipe pile and the discarded concrete if there is discarded concrete between the pile head of the steel pipe pile and the concrete foundation). The pile head of the steel pipe pile is annular, and only the edge portion contacts the concrete foundation. Therefore, there may be insufficient contact area to transmit the axial force from the steel pipe pile to the concrete foundation without causing damage to the steel pipe pile.

[0014] For example, the reinforcing structure may be concrete that occupies the internal space of the steel pipe pile provided within a predetermined range from the upper end of the steel pipe pile. The concrete may be cured inside the steel pipe pile or outside the steel pipe pile. Also, the concrete may exist inside the steel pipe pile before the steel pipe pile is driven into the ground, or may be formed inside the steel pipe pile after the steel pipe pile is driven into the ground. Specifically, the reinforcing structure may consist of a plate that closes the internal space of the steel pipe pile provided at a position a predetermined distance below the upper end of the steel pipe pile, and concrete that is placed and cured in the range above the plate inside the steel pipe pile. When there is concrete within a predetermined range from the upper end inside the steel pipe pile, the concrete occupying the vicinity of the upper end of the plate in the steel pipe pile becomes the reinforcing structure, and the surface of the uppermost part of the concrete (the part that horizontally closes the pile head of the steel pipe pile) contacts the concrete foundation, increasing the contact area between the steel pipe pile and the concrete foundation. Also, the reinforcing structure may be a metal plate fixed to the upper end of the steel pipe pile that closes the hole at the upper end of the steel pipe pile. In this case, when the metal plate contacts the concrete foundation, the contact area between the steel pipe pile and the concrete foundation increases. The metal constituting the metal plate is, for example, iron. The metal plate may be fixed to the steel pipe pile in a state of riding on the edge of the upper end of the steel pipe pile, or may be fixed to the steel pipe pile such that the edge of the upper end of the steel pipe pile and its upper surface are flush. When the metal plate is circular, its diameter can be equal to the outer shape of the steel pipe pile in the former case, and can be equal to the inner diameter of the steel pipe pile in the latter case. The reinforcing structure may be a thick-walled portion provided in a predetermined range from the upper end of the steel pipe pile and having a greater wall thickness than the portion below the reinforcing structure. In this case, when the upper surface of the thick-walled portion that is flush with the end face of the pile head of the steel pipe pile contacts the concrete foundation, the contact area between the steel pipe pile and the concrete foundation increases. The thick-walled portion can be configured, for example, by retrofitting a cylindrical metal member having an outer diameter corresponding to the inner diameter of the steel pipe pile to the steel pipe pile. The material of the thick-walled portion is, for example, iron. The reinforcing structure may be a metal plate having a predetermined length in the vertical direction and fixed inside the steel pipe pile in a point-symmetrical manner through the center of the steel pipe pile when the steel pipe pile is viewed in plan, and provided inside a predetermined range from the upper end of the steel pipe pile. In this case, when the upper surface of the metal plate that is flush with the end face of the pile head of the steel pipe pile contacts the concrete foundation, the contact area between the steel pipe pile and the concrete foundation increases. The plate can be fixed inside the steel pipe pile, for example, so as to form a cross when viewed in plan. The two plates located at the target positions passing through the center of the steel pipe pile may be a single piece. The material of the metal plate is, for example, iron.

[0015] The pile foundation structure described above can be used as the foundation of a building. The inventor of the present application also proposes, as one aspect of the present invention, a building including the pile foundation structure described above. An example of the building proposed by the inventor of the present application as the building of the present invention is a building including any of the pile foundation structures described above and an upper structure supported by the pile foundation structure, wherein the upper structure is a building adopting a wall structure. Since the wall structure supports the load of the upper structure of the building with walls, it does not have columns for supporting the load of the upper structure. Therefore, it is not necessary to correspond the position where the steel pipe piles in the pile foundation structure described above are driven into the ground to the position of the columns in the upper structure to be constructed later (the columns may not exist in the first place). On the other hand, the pile foundation structure as a whole can support the load of the upper structure adopting the wall structure. The invention of this building has the effects achieved by the pile foundation structure described above. Further, when the above-described pile foundation structure is combined with the upper structure of the wall structure, since the place where the steel pipe piles in the pile foundation structure should be arranged can be freely set (for example, when the upper structure is a ramen structure, the steel pipe piles need to be arranged directly below the columns, but there is no such limitation when the upper structure is a wall structure), the degree of freedom in design is high. In particular, when there are places where it is difficult to drive steel pipe piles into the ground, such as when there are underground obstacles, it is a great advantage that it is possible to drive the necessary steel pipe piles for the pile foundation structure while avoiding that place.

[0016] The inventor of the present application also proposes, as one aspect of the present invention, a construction method of a pile foundation structure used as a foundation for supporting an upper structure adopting a wall structure of a building. An example of the method is a construction method of a pile foundation structure used as a foundation for supporting an upper structure adopting a wall structure of a building, which includes a pile driving process of driving a predetermined number of steel pipe piles into the ground, and constructing a formwork on the steel pipe piles and placing and hardening concrete in the formwork to construct a concrete foundation made of concrete buried in the ground with a horizontal plane parallel to the horizontal end face at the upper end of the steel pipe piles as the bottom surface. In the pile driving process, the steel pipe piles are driven into a plurality of locations necessary for supporting the upper structure while avoiding underground obstacles in the ground.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2(A)

Figure 2(B)

Figure 2(C)

Figure 2(D)

Figure 2(E)

Figure 2(F)

Figure 2(G)

Figure 2(H)

Figure 3

Figure 4

Figure 5(A)

Figure 5(B)

Figure 5(C)

Figure 5(D)

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0018] Hereinafter, the first to third embodiments and their modified examples of the construction method for constructing the pile foundation structure of the present invention will be described with reference to the drawings. In the description of each embodiment, common objects shall be given common reference numerals, and common descriptions may be omitted as appropriate.

[0019] ≪First Embodiment≫ The pile foundation structure constructed by the construction method of the first embodiment has a concrete foundation similar to an independent foundation in a direct foundation. For example, in the plan view of FIG. 1, 1 is the position where the column included in the upper structure adopting the ramen structure of the building will be erected later, and 2A is the pile foundation structure body. The combination of six pile foundation structure bodies 2 is the pile foundation structure 2. In FIG. 1 surrounded by six columns, the horizontally long rectangular range is the range where the upper structure of the building will be erected later. Although not limited to this, in this embodiment, the steel pipe pile described later is positioned directly below the position 1 where the column will be erected. However, there may be a pile foundation structure body 2A including a steel pipe pile at other positions. When the upper structure is not a ramen structure, for example, when a wall structure is adopted, the position and number of the pile foundation structure bodies 2A may be completely different from those in the case of FIG. 1.

[0020] Describe how each pile foundation structure 2A is constructed. First, in the ground 10, excavate the area where the superstructure of the building will generally be erected later to the depth where the pile head should be located. Then, drive the steel pipe pile 20 (Fig. 2(A)). Note that Figs. 2(A) to (D) are cross-sectional views including the center of the steel pipe pile 20 in the vicinity where the pile foundation structure 2A is constructed. The steel pipe pile 20, excluding the reinforcement structure described later, may be a known or well-known one, or more precisely, a commercially available one. The steel pipe pile 20 is selected according to the properties of the ground and the weight of the superstructure of the building, etc. The steel pipe pile 20 is, for example, a support pile. At the upper end of the steel pipe pile 20 or within a predetermined range from the upper end, a reinforcement structure is provided that contributes to the transmission of the axial force from the building through the steel pipe pile 20 to the ground. The reinforcement structure is basically made on the steel pipe pile 20 before the steel pipe pile 20 is driven into the ground 10, but it may also be provided on the steel pipe pile 20 after the steel pipe pile 20 is driven into the ground 10.

[0021] An example of the reinforcement structure will be described with reference to Fig. 3. Figs. 3 are all cross-sectional views of the steel pipe pile 20. However, Fig. 3(F) is a plan view of the steel pipe pile 20 shown in Fig. 3(E). The reinforcement structure is for efficiently transmitting the upward axial force transmitted from the steel pipe pile 20 to an independent foundation, which is a type of concrete foundation described later, and for increasing the contact area between the steel pipe pile 20 and the bottom surface of the independent foundation. The reinforcement structure shown in Fig. 3(A) is composed of the concrete 22 that is placed and hardened in the space inside the steel pipe pile 20 above the plate 21 that closes the internal space of the steel pipe pile 20 and is provided at a predetermined position near the upper end of the steel pipe pile 20. The timing of placing the concrete 22 into the steel pipe pile 20 may be before or after driving the steel pipe pile 20 into the ground 10. When placing the concrete 22 into the steel pipe pile 20 after driving the steel pipe pile 20 into the ground, it is also possible to omit the plate 21 and fill the concrete 22, for example, to the lower end of the steel pipe pile 20 and then harden it. Further, the concrete 22 may be formed in a columnar shape outside the steel pipe pile 20 in a state adapted to the inner diameter of the steel pipe pile 20. In that case, the columnar concrete 22 is fitted onto the upper part of the steel pipe pile 20 at an appropriate timing before and after driving the steel pipe pile 20 into the ground 10. Also in this case, the plate 21 becomes unnecessary. The columnar concrete 22 may be firmly fixed to the steel pipe pile 20, for example, by screwing it with the tip of a bolt passed through the steel pipe pile 20. In any case, when a reinforcing structure in which the concrete 22 is disposed at least on the uppermost end side of the steel pipe pile 20 is adopted in the steel pipe pile 20, the surface of the uppermost part of the concrete 22 (the part that horizontally closes the pile head of the steel pipe pile 20) contacts the independent foundation described later, so that the contact area between the steel pipe pile 20 and the concrete foundation, which is a kind of independent foundation, increases. The reinforcing structures shown in FIGS. 3(B) and (C) are metal plates 23 and 24 fixed to the upper end of the steel pipe pile 20 and closing the holes at the upper end of the steel pipe pile 20. In this case, the contact area between the steel pipe pile 20 and the concrete foundation increases because the metal plates 23 and 24 contact the concrete foundation. The metal constituting the metal plates 23 and 24 is, for example, iron. The metal plate may be fixed to the steel pipe pile 20 in a state of straddling the edge of the upper end of the steel pipe pile 20 (FIG. 3(C)), or may be fixed inside the upper end of the steel pipe pile 20 so that the edge and the upper surface of the upper end of the steel pipe pile 20 are flush (FIG. 3(B)). Both the metal plates 23 and 24 are circular, and the diameter thereof can be equal to the outer shape of the steel pipe pile 20 as shown in FIG. 3(C) and equal to the inner diameter of the steel pipe pile 20 as shown in FIG. 3(B). The fixing of the metal plates 23 and 24 to the steel pipe pile 20 may be performed in any manner as long as the strength is guaranteed. For example, it can be performed by welding or screwing with bolts. The reinforcing structure shown in FIG. 3(D) is a thick part 25 provided in a predetermined range from the upper end of the steel pipe pile 20 and having a greater thickness than the part below the reinforcing structure. In this case, the upper surface of the thick-walled portion 25 that is flush with the end face of the head of the steel pipe pile 20 comes into contact with the concrete foundation, thereby increasing the contact area between the steel pipe pile 20 and the concrete foundation. The thick-walled portion 25 can be created, for example, by attaching a cylindrical metal member having an outer diameter corresponding to the inner diameter of the steel pipe pile 20 to the steel pipe pile 20. The material of the thick-walled portion 25 is, for example, iron. The fixing of the thick-walled portion 25 to the steel pipe pile 20 can be carried out in any way as long as the strength is guaranteed. For example, it can be carried out by welding or screwing with bolts. The reinforcement structure shown in FIGS. 3(E) and (F) is a metal plate 26 having a predetermined length in the vertical direction, which is provided inside a predetermined range from the upper end of the steel pipe pile 20 and is fixed inside the steel pipe pile 20 so as to be point-symmetrical about the center of the steel pipe pile 20 when viewed in plan. In this case, the upper surface of the metal plate 26 that is flush with the end face of the head of the steel pipe pile 20 comes into contact with the concrete foundation, thereby increasing the contact area between the steel pipe pile 20 and the concrete foundation. In the example shown in FIGS. 3(E) and (F), the plate 26 can be fixed inside the steel pipe pile 20 so as to form a cross when viewed in plan. The plate 26 may be arranged inside the steel pipe pile 20 so as to radiate in four directions like this, but for example, it may be arranged so as to radiate from the center in two directions, six directions, eight directions, etc., in any appropriate number of two or more. The two plates 26 existing at symmetrical positions with respect to the center of the steel pipe pile 20 may be a single piece. The metal plate 26 is, for example, made of iron. The fixing of the plate 26 to the steel pipe pile 20 can be carried out in any way as long as the strength is guaranteed. For example, it can be carried out by welding or screwing with bolts.

[0022] After driving the steel pipe pile 20 into the ground, an independent foundation 30 is then constructed on the steel pipe pile 20 (FIG. 2(B)). Thus, the pile foundation structure 2 is completed. The isolated foundation 30 is a type of concrete foundation and is made of concrete. In this embodiment, the isolated foundation 30 is in the shape of a rectangular parallelepiped. The top of the steel pipe pile 20 is a horizontal plane, and the bottom surface of the isolated foundation 30 is a plane parallel to that plane. The isolated foundation 30 does not engulf the top of the steel pipe pile 20. Although not limited to this, in this embodiment, the isolated foundation 30 is constructed such that the steel pipe pile 20 is located directly below the center of the isolated foundation 30 when viewed in plan. The isolated foundation 30 is constructed by placing concrete inside a assembled formwork and curing the placed concrete.

[0023] In this embodiment, the pile foundation structure 2 including the isolated foundation 30 is constructed by performing the above operations at six locations. In the case of an isolated foundation in a direct foundation, the isolated foundations are often connected by an underground beam or a beam foundation. However, in the pile foundation structure 2 in this embodiment, such an underground beam or beam foundation is not required. Note that, as shown in FIGS. 2(C) and 2(D), a layered discarded concrete 31 can be provided in the pile foundation structure 2. FIG. 2(C) shows the case where the discarded concrete 31 is constructed after driving the steel pipe pile 20 into the ground 10 and before constructing the isolated foundation 30, and FIG. 2(D) shows the case where the discarded concrete 31 is constructed after constructing the isolated foundation 30. It is also possible to provide the discarded concrete 31 in the second and third embodiments. In the example of FIG. 2(C), the discarded concrete 31 is constructed to cover the entire surface of the excavated ground 10, whereas in the example of FIG. 2(D), the discarded concrete 31 is constructed only around the isolated foundation 30 of the excavated ground 10. The discarded concrete 31 may not exist in the first place, and it is free to provide the discarded concrete 31 within any of the ranges described above when providing it. Each steel pipe pile 20 shown in FIGS. 2(A) to 2(D) had a reinforcement structure reinforced by concrete 22 as shown in FIG. 3(A). In this case, the concrete 22 inside the steel pipe pile 20 was in contact with the disposable concrete 31 shown in FIG. 2(C). Therefore, as in the example shown in FIG. 2(C), when constructing the disposable concrete 31 after driving the steel pipe pile 20 into the ground 10 and before constructing the isolated footing 30, the disposable concrete and the concrete 22 inside the steel pipe pile 20 can be made together by one placement of concrete. In this case, if the slab 21 is omitted, the concrete 22 will be filled up to the lower end of the steel pipe pile 20 or the vicinity thereof. The disposable concrete 31 is meaningful in terms of leveling and ensuring the ease of work for workers, similar to the conventional one.

[0024] In the description so far, it has been described that the shape of the isolated footing 30 is a rectangular parallelepiped. However, the shape of the isolated footing 30 does not have to be a rectangular parallelepiped. For example, the isolated footing 30 can be in the shape of a frustum of a square pyramid as shown in the side sectional view of FIG. 2(E) and the plan view of FIG. 2(F). Of course, it is not limited to this, but the isolated footing 30 shown in FIGS. 2(E) and 2(F) is a square in which the center overlaps when viewed in plan for the bottom surface and the top surface, and all four side surfaces are the same trapezoid. The isolated footing 30 can also be configured in a shape in which a rectangular parallelepiped portion having an upper surface with the same size and shape as the bottom surface of the frustum of a square pyramid is connected under the frustum of a square pyramid as shown in the side sectional view of FIG. 2(G) and the plan view of FIG. 2(H). Of course, it is not limited to this, but the isolated footing 30 shown in FIGS. 2(G) and 2(H) is a similar-shaped rectangle, more specifically a square, in which the center overlaps when viewed in plan for the bottom surface and the top surface. When the isolated footing 30 described in this paragraph has the same bottom area as the rectangular parallelepiped-shaped isolated footing 30 and a common height, the amount of concrete used can be suppressed compared to the rectangular parallelepiped-shaped isolated footing 30.

[0025] On the pile foundation structure 2 in the first embodiment, the superstructure of the building is constructed. The superstructure of the building having the pile foundation structure 2 may adopt a wall structure. Examples of such buildings are, for example, single-family houses and condominiums. The superstructure adopting the wall structure does not have at least columns that support the load of the superstructure. Therefore, even if the superstructure adopting the wall structure has columns, each pile foundation structure 2A does not need to be located under the columns and does not need to be present at the position shown in FIG. 1. Each pile foundation structure 2A supports, for example, the floor slab and walls of the superstructure adopting the wall structure, and as a result, the load of the superstructure is supported. For example, the pile foundation structures 2A are formed at a plurality of locations necessary to support the superstructure while avoiding underground obstacles (such as large rocks) in the ground 10, and the steel pipe piles 20 are driven into those positions.

[0026] ≪Second Embodiment≫ The pile foundation structure constructed by the construction method of the second embodiment makes the concrete foundation similar to the beam foundation in the direct foundation. For example, in the plan view of FIG. 4, 1 is the position where columns included in the superstructure adopting the ramen structure of the building are to be erected later, and 3A is the pile foundation structure. The pile foundation structure 3A includes at least two steel pipe piles described later and is long. In the example of FIG. 4, there are two pile foundation structures 3A each including three steel pipe piles running in the horizontal direction, and three pile foundation structures 3A each including two steel pipe piles running in the vertical direction. The combination of these five pile foundation structures 3A is the pile foundation structure 3. In FIG. 4 surrounded by six columns, the horizontally long rectangular range is the range where the superstructure of the building will be erected later. Although not limited to this, in this embodiment, the steel pipe piles described later are located directly below the position 1 where the columns are to be erected. However, steel pipe piles may exist at other positions, and pile foundation structures 3A other than those shown including the steel pipe piles may exist. When the superstructure is not of the ramen structure, for example, when a wall structure is adopted, the position and number of the pile foundation structures 3A may be completely different from those in the case of FIG. 4.

[0027] Describe how each pile foundation structure 3A is constructed. First, in the ground 10, the area where the superstructure of the building will generally be erected later is excavated to the depth where the pile heads should be located. Then, the steel pipe piles 20 are driven in (Fig. 5(A)). Note that Fig. 5 is a cross-sectional view along a plane perpendicular to the length of the pile foundation structure 3A including the center of the steel pipe piles 20 in the vicinity where the pile foundation structure 3A is constructed. The steel pipe piles 20 are general ones except for the reinforcement structure. Similar to the first embodiment, a reinforcement structure is provided in a predetermined range from the upper end of the steel pipe piles 20. The reinforcement structure is as described in the first embodiment.

[0028] After driving the steel pipe piles 20 into the ground, next, the beam foundation 40 is constructed on the steel pipe piles 20 (Fig. 5(B)). Thus, the pile foundation structure 3 is completed. The beam foundation 40 is a type of concrete foundation and is made of concrete. In this embodiment, the beam foundation 40 has a long rectangular parallelepiped shape. The pile heads of the steel pipe piles 20 are horizontal planes, and the bottom surfaces of the respective beam foundations 40 are planes parallel to that plane. The beam foundation 40 does not swallow the pile heads of the steel pipe piles 20. Although not limited to this, in this embodiment, the beam foundation 40 is constructed such that the steel pipe piles 20 are located directly below the center in the width direction of the beam foundation 40 when viewed in plan. The beam foundation 40 is constructed by placing concrete inside a formwork and hardening the placed concrete.

[0029] The concrete placement during the construction of the beam foundation 40 may be carried out all at once for the beam foundations 40 included in all the pile foundation structures 3A. At least, the concrete placement for the beam foundations 40 included in the pile foundation structures 3A that are in contact with each other can be carried out together. In this embodiment, by making five pile foundation structures 3A, the pile foundation structure 3 is constructed. As already explained, the use of waste concrete is also possible in the second embodiment. Although the beam foundation 40 has been described as having a long rectangular parallelepiped shape, it may be provided with a footing 41 as shown in Fig. 5(C). The footing 41 projects from the beam foundation 40 by a predetermined length in its width direction and has a predetermined thickness smaller than the height of the beam foundation 40. The footing 41 can be constructed integrally with the beam foundation 40 by appropriately shaping the formwork. That is, a certain beam foundation 40 and the footing 41 projecting therefrom can be constructed by a single placement of concrete. The beam foundation 40 having the footing 41 may have a cross-section perpendicular to the length direction as shown in Fig. 5(D). The dashed line in Fig. 5(D) is conceptual. The cross-section of the beam foundation 40 shown in Fig. 5(D) has a shape in which horizontal rectangles are arranged under a trapezoid, and is hexagonal as a whole. Although there is no externally exposed footing 41 as shown in Fig. 5(C) in this beam foundation 40, it can be understood that the footing 41 exists under the triangular portions existing on both shoulders of the beam foundation 40 indicated by the dashed line. Of course, the beam foundation 40 shown in Fig. 5(D) can also be constructed by a single placement of concrete.

[0030] The superstructure of the building is constructed on the pile foundation structure 3 in the second embodiment. The superstructure of the building having the pile foundation structure 3 may adopt a wall structure. Examples of such buildings are, for example, single-family houses and condominiums. The superstructure adopting the wall structure does not have at least columns that support the load of the superstructure. Therefore, even if the superstructure adopting the wall structure has columns, each pile foundation structure body 3A does not need to be located under the columns and does not need to be located at the position shown in Fig. 4. Each pile foundation structure body 3A supports, for example, the floor slab and walls of the superstructure adopting the wall structure, and as a result, the load of the superstructure is supported. For example, the steel pipe piles 20 are driven into a plurality of locations necessary to support the superstructure while avoiding underground obstacles in the ground 10, and the position of the beam foundation 40 is designed according to the position of the steel pipe piles 20.

[0031] <<Third Embodiment>> The pile foundation structure constructed by the construction method of the third embodiment has a concrete foundation similar to the mat foundation in the direct foundation. For example, in the plan view of FIG. 6, 1 is the position where columns included in the superstructure adopting the ramen structure of the building will be erected later, and 4 is the pile foundation structure. The pile foundation structure 4 includes at least two steel pipe piles and is plate-shaped. The pile foundation structure 4 in this embodiment is integrally configured. In FIG. 6 surrounded by six columns, the horizontally long rectangular range is the range where the superstructure of the building will be erected later. Although not limited to this, in this embodiment, the steel pipe piles described later are located directly below the position 1 where the columns will be erected. However, steel pipe piles may exist at other positions. In any case, the pile foundation structure 4 will include a plurality of steel pipe piles. When the superstructure is not a ramen structure, for example, when a wall structure is adopted, the position and number of steel pipe piles driven may be completely different from those in the case of FIG. 6.

[0032] An explanation will be given of how the pile foundation structure 4 is constructed. First, in the ground 10, the range where the superstructure of the building will generally be erected later is excavated to the depth where the pile heads should be located. Then, the steel pipe piles 20 are driven (FIG. 7(A)). Note that FIG. 7 is a side sectional view of the vicinity of an arbitrary steel pipe pile 20 included in the pile foundation structure 4. The steel pipe piles 20 are general ones except for the reinforcement structure. Similar to the first embodiment, a reinforcement structure is provided in a predetermined range from the upper end of the steel pipe piles 20. The reinforcement structure is as described in the first embodiment.

[0033] After driving the steel pipe piles 20 into the ground, next, a bottom foundation 50 is constructed on the steel pipe piles 20 (FIG. 7(B)). Thus, the pile foundation structure 4 is completed. The chassis foundation 50 is a type of concrete foundation and is made of concrete. In this embodiment, the chassis foundation 50 is plate-shaped with a predetermined thickness. All the steel pipe piles 20 are positioned below the chassis foundation 50. The pile heads of the steel pipe piles 20 are in a horizontal plane, and the bottom surface of the chassis foundation 50 is a plane parallel to that plane. The chassis foundation 50 does not engulf the pile heads of the steel pipe piles 20. The chassis foundation 50 is constructed by placing concrete inside the assembled formwork and curing the placed concrete. The formwork is installed so as to surround the outer periphery of the chassis foundation 50.

[0034] The placement of concrete during the construction of the chassis foundation 50 usually ends in one go. It is also possible to construct the chassis foundation 50 by dividing it through multiple placements of concrete. As already explained, it is possible to use waste concrete even in the third embodiment.

[0035] On top of the pile foundation structure 4 in the third embodiment, the superstructure of the building is constructed. The superstructure of the building having the pile foundation structure 4 may adopt a wall structure. Examples of such buildings are, for example, single-family houses and condominiums. The superstructure adopting the wall structure does not have at least columns that support the load of the superstructure. Therefore, even if the superstructure adopting the wall structure has columns, the steel pipe piles 20 in the pile foundation structure 4 do not need to be positioned under the columns and do not need to be present at the positions shown in Fig. 6. For example, the steel pipe piles 20 in the pile foundation structure 4 will be driven into a plurality of locations necessary to support the superstructure while avoiding underground obstacles in the ground 10.

Explanation of reference numerals

[0036] 1 Position where a column is planned to be erected 2 Pile foundation structure 2A Pile foundation structure body 3 Pile foundation structure 3A Pile foundation structure body 4 Pile foundation structure 10 Ground 20 Steel pipe pile 21 Plate 22 Concrete 23 Plate 24 Plate 25 Thickness Portion 26 Plate 30 Independent Foundation 40 Beam Foundation 50 Chassis Foundation

Claims

1. A pile foundation structure used as a foundation for supporting the superstructure of a building, a steel pipe pile driven into the ground, and a concrete foundation made of concrete and buried in the ground, having a horizontal plane parallel to the horizontal end face at the upper end of the steel pipe pile as the bottom surface and placed on the steel pipe pile, The pile foundation structure having.

2. The plurality of steel pipe piles, The concrete foundation is the same number of independent foundations as the number of the steel pipe piles independent of each other, each placed on each of the steel pipe piles, The pile foundation structure according to Claim 1.

3. The independent foundation is in a rectangular parallelepiped shape, The pile foundation structure according to Claim 2.

4. The plurality of steel pipe piles, The concrete foundation is a linear beam foundation in plan view, placed on at least two of the steel pipe piles, The pile foundation structure according to Claim 1.

5. The beam foundation is in a rectangular parallelepiped shape, The pile foundation structure according to Claim 4.

6. The beam foundation is provided with a footing having a predetermined thickness and wider than the beam foundation at its lower end, so as to be a slab foundation having a substantially T-shaped cross section, The pile foundation structure according to Claim 5.

7. The plurality of steel pipe piles, The concrete foundation is a chassis foundation having a planar spread and integrated in a plate shape, placed on all of the steel pipe piles, The pile foundation structure according to Claim 1.

8. A reinforcing structure that contributes to the transmission of the axial force from the superstructure of the building through the steel pipe pile to the ground is provided at the upper end of the steel pipe pile or in a predetermined range from the upper end, The pile foundation structure according to any one of Claims 1 to 7.

9. The reinforcing structure is concrete that occupies the internal space of the steel pipe pile, provided in a predetermined range from the upper end of the steel pipe pile, The pile foundation structure according to Claim 8.

10. The reinforcing structure includes a plate that closes the internal space of the steel pipe pile, provided at a position a predetermined distance below the upper end of the steel pipe pile, and concrete placed and hardened in a range above the plate inside the steel pipe pile, The pile foundation structure according to Claim 9.

11. The reinforcing structure is a metal plate that closes the hole at the upper end of the steel pipe pile, fixed to the upper end of the steel pipe pile, The pile foundation structure according to Claim 8.

12. The reinforcing structure is a thick-walled portion provided in a predetermined range from the upper end of the steel pipe pile and thicker than the portion below the reinforcing structure, The pile foundation structure according to Claim 8.

13. The reinforcing structure is a metal plate with a predetermined length in the vertical direction, which is provided inside a predetermined range from the upper end of the steel pipe pile and is fixed in the steel pipe pile so as to be point-symmetrical about the center of the steel pipe pile when the steel pipe pile is viewed in plan view. The pile foundation structure according to claim 8.

14. The pile foundation structure according to any one of claims 1 to 13, an upper structure supported by the pile foundation structure, comprising a building, wherein the upper structure employs a wall structure. Building.

15. A construction method of a pile foundation structure used as a foundation for supporting an upper structure that employs a wall structure of a building, a pile driving process of driving a predetermined number of steel pipe piles into the ground, a concrete foundation construction process of constructing a concrete foundation made of concrete embedded in the ground, with a horizontal plane parallel to the horizontal end face at the upper end of the steel pipe pile as the bottom surface, by constructing a formwork on the steel pipe pile and placing and curing concrete in the formwork, having, in the pile driving process, driving steel pipe piles into a plurality of locations necessary to support the upper structure while avoiding underground obstacles in the ground. Construction method of pile foundation structure.

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