Foundation structure and its construction method

Abstract

To provide a foundation structure which can prevent shear fracture, in a semi-rigid joint type joint part between an existing pile and a foundation structure part.SOLUTION: A reinforced concrete structure foundation having a recess 21 on a lower surface is foundation structure K mounted on a pile head part of an existing pile 1 driven in the ground G in the recess 21. The recess 21 includes a form 3 which is formed so as to be wider toward the lower side, is provided integrally with the recess 21, and has a flange part 32b on its circumference.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a foundation structure in which a structural foundation is placed on the pile heads of precast piles installed in the ground, and a method for constructing the same. [Background technology]

[0002] Aoshima et al., one of the present inventors, have developed the following construction method for a so-called semi-rigid joint type foundation structure (a foundation structure in which a structural foundation is placed on the pile head of a prefabricated pile installed in the ground; hereinafter, this may be simply referred to as a "semi-rigid joint structure") that can reduce bending moments occurring at the pile head while ensuring high shear force transmission capacity during an earthquake. Specifically, this method for constructing a semi-rigid joint structure includes the steps of: embedding a prefabricated pile, the pile head of which has a jig that engages with a rotary press-in device, into the ground using the rotary press-in device; removing the jig; covering the pile head with a formwork with a sloping inner surface to form a gap that expands downward between the side of the pile head and the inner surface of the formwork; pouring leveling concrete around the formwork; and pouring foundation concrete that will become the structural foundation on top of the hardened leveling concrete (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-23602 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in foundation structures constructed using conventional construction methods, when horizontal forces are applied during earthquakes or strong winds, etc. (hereinafter referred to as "earthquakes, etc."), shear failure occurs at the joint between the underside of the structure's foundation and the pile head of the prefabricated pile, and there is also the possibility of punching shear failure occurring due to the application of localized concentrated loads, so measures to address this issue were required.

[0005] The present invention has been made to solve the above problems, and aims to provide a foundation structure and a construction method thereof that can prevent shear failure at the joint between the underside of a structure foundation and the pile head of a precast pile, assuming a semi-rigid joint type foundation structure. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a foundation structure (hereinafter referred to as "this foundation structure") characterized in that a reinforced concrete structural foundation having a recess on its underside is placed on the heads of prefabricated piles that have been driven into the ground in the recess, the recess being formed to widen downward, and the recess being provided with a formwork having a flange on its periphery that is integrally formed with the recess. In addition, a cage-shaped restraining bar is provided so as to surround the upper surface of the formwork, and the restraining bar is characterized by comprising a plurality of vertical bars and horizontal bars surrounding the plurality of vertical bars. Furthermore, each of the vertical reinforcements is arranged so as to extend in the vertical direction of the lowermost end reinforcement of the structure foundation.

[0007] Here, "placing" means that in a method of constructing a foundation structure in which a structural foundation (regardless of the shape or form of the structural foundation) is placed on the head of a prefabricated pile that has been driven (buried) into the ground, in order to support the structural foundation, the structural foundation is simply placed on top of the head of the prefabricated pile, and is in a semi-rigid joint state in which the degree of fixation of the joint is reduced and rotation is permitted. The explanations of the terms above and others are common to the present basic structure and the method for constructing the present basic structure described below.

[0008] The formwork must be frustum-shaped (a shape inclined so that the inner peripheral surface becomes wider downward), have a flange formed on the periphery (lower edge) of the lower surface, and have a space inside. Furthermore, it is preferable that the formwork be shaped like a truncated cone with an upper surface, have an open bottom surface, have an internal space, and have a flange formed on the edge of the circumferential surface of the bottom surface. There are no restrictions on the dimensions and materials of the formwork (including the flange), but it is preferable to use a metal such as steel to withstand the lateral pressure of the concrete and prevent breakage.

[0009] The formwork may also have a disk-shaped upper surface portion and a side portion provided on the outer peripheral edge of the upper surface portion, the inner diameter of which gradually increases downward, and the flange portion may be formed on the lower peripheral edge of the side portion. The outer peripheral surface of the side portion may have a marking along the lower edge thereof.

[0010] In addition, a crushed stone layer may be formed on the ground, and the gap between the lower edge of the formwork and the upper surface of the crushed stone layer may be closed by piling up ground material around the outer periphery of the lower end of the formwork. Furthermore, a layer of leveling concrete may be provided around the formwork on top of the crushed stone layer.

[0011] The restraining reinforcement is also installed to resist the shear force that occurs near the recess in the foundation of the structure (near the pile head joint) when a horizontal force is applied. Therefore, it is necessary to install it appropriately so that it surrounds the vicinity of the top surface of the formwork. Therefore, to achieve the above-mentioned effect, it is necessary to arrange vertical reinforcement (anchoring reinforcement installed vertically) and horizontal reinforcement (transverse reinforcement installed horizontally), and the number, standard, weight, installation method, etc. of these reinforcement can be determined appropriately. The horizontal reinforcement is a transverse reinforcement formed by bending steel bars into a closed shape, and it is preferable to use spiral reinforcement and multiple ring-shaped hoop reinforcement.

[0012] In addition, the lowest bottom reinforcement in a structural foundation refers to the reinforcing bar that is placed at the bottom in the vertical direction when there are multiple reinforcing bars that make up the bottom reinforcement placed in the structural foundation. Regarding the arrangement of vertical reinforcement, "arranged so as to extend in the vertical direction of the lowest reinforcing bar in the foundation of the structure" means that the upper end of the vertical reinforcement is arranged above the lowest reinforcing bar, and the lower end of the vertical reinforcement is arranged below the lowest reinforcing bar.

[0013] According to this foundation structure, a cage-shaped restraining bar is formed in the structure foundation so as to surround the upper surface of the formwork, and each vertical bar that makes up the restraining bar is arranged so that it extends in the vertical direction of the lowest lower end bar in the structure foundation, thereby effectively preventing shear failure that occurs near the recess in the structure foundation (near the pile head joint) during an earthquake, etc.

[0014] The present invention also provides a method for constructing a foundation structure in which a reinforced concrete structure foundation is placed on the pile heads of precast piles set in the ground, the method comprising the steps of: a precast pile driving step of driving the precast piles into the ground; a form setting step of covering the pile heads with a frustum-shaped formwork having a flange formed on its periphery (hereinafter, a formwork having a flange formed thereon may be referred to as a "flanged formwork") to form a gap between the side surface of the pile head and the inner peripheral surface of the formwork; a leveling concrete pouring step of pouring leveling concrete around the formwork; and a structure foundation concrete pouring step of pouring foundation concrete for the structure foundation on the leveling concrete while the formwork is constrained by the leveling concrete (hereinafter, referred to as "the construction method"). (The construction method may also include a constraining bar reinforcing bar arrangement step of arranging cage-shaped constraining bars so as to surround the upper surface of the formwork.)

[0015] In addition, in the formwork installation step, the heads of the prefabricated piles may be covered with the formwork, and then the formwork may be temporarily fixed to the heads of the piles. Furthermore, in the prefabricated pile driving process, a crushed stone layer may be formed on the ground, and in the formwork installation process, after the formwork is temporarily fixed to the pile head, ground material may be placed around the outer periphery of the lower end to close the gap that exists between the lower edge of the formwork and the upper surface of the crushed stone layer.

[0016] Furthermore, in this construction method, the restraining reinforcement comprises a plurality of vertical reinforcements and horizontal reinforcements surrounding the plurality of vertical reinforcements, and by arranging the vertical reinforcements so that they extend in the vertical direction of the lowest end reinforcement in the foundation of the structure, this is preferable because it improves workability.

[0017] Here, ground materials are a general term for crushed stone (gravel), sand, clay, soil used on-site, etc. In addition, when placing ground material around the formwork, an appropriate method can be used depending on the conditions of the target site, such as piling crushed stone or the like around the perimeter of the formwork and burying the bottom end of the formwork in the ground (floor surface).

[0018] Furthermore, in the prefabricated pile driving process, there are no restrictions on the method for driving the prefabricated pile into the ground, but it is preferable to bury a prefabricated pile with a jig that engages with a rotary driving device protruding from the pile head using the rotary driving device, and then remove the jig for the rotary driving device attached to the prefabricated pile before covering the pile head with formwork, as this prevents noise during construction and eliminates the problem of the jig restricting the rotation of the pile head of the prefabricated pile after driving.

[0019] This construction method includes a reinforcing bar placement process in which cage-shaped reinforcing bars are placed around the top surface of the formwork, making it possible to easily construct this foundation structure that can prevent shear failure. In addition, the formwork used in the formwork installation process is frustum-shaped and has a flange formed around the periphery of its underside, making it easy to handle during construction, which helps to ensure safety during construction.

[0020] Furthermore, since the leveling concrete is poured using a formwork with a flange, the presence of the flange makes it less likely for the formwork to shift or deform when pouring the concrete for the structure's foundation, effectively preventing concrete and ground materials from entering the gaps.

[0021] In addition, in this construction method, if the formwork is fixed to the pile head using fasteners before the leveling concrete pouring process, and the fasteners are removed before the foundation concrete pouring process, this can reliably prevent any slight shifting of the formwork that may occur when pouring the leveling concrete, and is therefore preferable because it can more reliably achieve the joint condition envisioned at the time of design.

[0022] Furthermore, in this construction method, the outer peripheral surface of the formwork has markings along its lower edge, and if ground material or leveling concrete is placed on the outer periphery of the lower end of the formwork up to the position of the markings before the leveling concrete pouring process, this facilitates construction and is advantageous because it prevents concrete from flowing into the gap formed between the side of the pile head and the inner peripheral surface of the formwork, thereby ensuring a gap around the pile head. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a foundation structure and a construction method thereof that can prevent shear failure at the joint between a semi-rigid joint type prefabricated pile and a foundation structure. [Brief explanation of the drawings]

[0024] [Figure 1] 1A and 1B are cross-sectional side views showing the foundation structure of the present invention, where FIG. 1A shows the structure under normal conditions and FIG. 1B shows the structure under an earthquake. [Figure 2] FIG. 1(a) is a perspective view showing a precast pile used in the foundation structure of the present invention, and FIG. 1(b) is a perspective view showing a formwork used in the foundation structure of the present invention. [Figure 3]3(a) is a perspective view showing a cage-shaped restraining bar used in the foundation structure of the present invention, and FIG. 3(b) is an enlarged view of the X portion of FIG. 3(a). [Figure 4] FIG. 10 is a side cross-sectional view showing another embodiment of the foundation structure of the present invention. [Figure 5] 5(a) to 5(c) are side cross-sectional views illustrating a prefabricated pile driving step in the foundation structure construction method of the present invention. [Figure 6] 1A and 1B are cross-sectional side views for explaining the method for constructing a foundation structure of the present invention, in which FIG. 1A shows a formwork installation step, and FIG. 1B shows a leveling concrete pouring step. [Figure 7] FIG. 10 is a side cross-sectional view showing another embodiment of the formwork installation step in the foundation structure construction method of the present invention. [Figure 8] 1A and 1B are side cross-sectional views for explaining the method for constructing a foundation structure of the present invention, in which FIG. 1A shows a constraining reinforcement arrangement step, and FIG. 1B shows a structure foundation concrete pouring step. DETAILED DESCRIPTION OF THE INVENTION

[0025] An example of an embodiment of the present foundation structure and construction method will be described in detail below with reference to the drawings. In the description based on the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. For the sake of illustration, the cage-shaped restraining reinforcement 40 is shown simplified in Figures 1(a), 1(b), 4, 8(a), and 8(b).

[0026] [Main basic structure] First, before explaining the construction method, the basic structure K will be explained. This foundation structure K is a semi-rigid joint type foundation structure that reduces the bending moment applied to the pile head while ensuring shear force transmission capacity, and is a structure in which pile cap 2, which is the foundation of a reinforced concrete structure, is placed on the pile head of prefabricated pile 1 driven into the ground G (Figure 1(a)).

[0027] (prefabricated piles) The prefabricated pile 1 comprises a hollow cylindrical main body 11 and an annular end plate 12 attached to the upper end surface of the main body 11 (FIG. 2(a)). In this embodiment, the main body 11 is reinforced with PC steel bars (not shown) in the longitudinal direction (vertical direction). The main body 11 may be made of any material as long as it can obtain the required strength, and may be made of prestressed concrete, concrete with a steel shell, steel pipe, etc.

[0028] The end plate 12 is made of steel, and is fixed to the upper end surface of the main body 11 by embedding anchors (not shown) protruding from the bottom surface into the main body 11. The end plate 12 also has a plurality of female screw holes 12a formed at predetermined intervals around the circumferential direction (FIG. 2(a) shows a jig 13 used in the prefabricated pile driving step of this construction method). When the main body 11 is made of steel, the end plates 12 are usually fixed by welding, but in some cases the end plates 12 can be omitted.

[0029] (Pile cap) The pile cap 2 is a structure made of reinforced concrete, and has a truncated cone-shaped recess 21 (a recess that widens downward) formed on its bottom surface. That is, the formwork 3 is placed over the top of the precast pile 1, and then the foundation concrete that will become the pile cap 2 is poured. With the above-mentioned configuration, the formwork 3 and the foundation concrete are integrated, and a recess 21 having the same shape as the space in the formwork 3 is formed.

[0030] The formwork 3 has a disk-shaped upper surface 31 that abuts the upper end surface (upper surface of the end plate 12) of the precast pile 1, whose inner surface is inclined, and a side portion 32 that surrounds the head of the precast pile 1, and has an appearance of a truncated cone (Figure 2(b)).

[0031] The upper surface portion 31 has the same planar shape as the upper end surface of the pile head of the prefabricated pile 1. The upper surface portion 31 has through holes 31a for temporarily fixing the end plate 12 formed in a plurality of locations (two locations in this embodiment) corresponding to the female screw holes 12a in some of the end plates 12. The side portion 32 is provided on the outer peripheral edge of the upper surface portion 31, and its inner diameter gradually increases downward, with a flange portion 32b formed on the periphery of the lower surface.

[0032] Furthermore, on the outer peripheral surface of the side portion 32, a mark 32a is provided along the lower edge of the formwork 3 as a guide when embedding the side portion 32 in the crushed stone layer S. It is preferable that the mark 32a be formed at a position at least 2 cm above the lower edge of the formwork 3. In this embodiment, the mark 32a is formed continuously around the entire periphery of the side portion 32, but this is not limitative and the mark may be formed intermittently.

[0033] The head of the precast pile 1 is arranged in contact with the inner surface of the upper surface 31 of the formwork 3, and the presence of the formwork 3 forms a gap E around the head of the precast pile 1.

[0034] Furthermore, a crushed stone layer S of a predetermined thickness is formed on the ground G, and a leveling concrete layer C of a predetermined thickness is provided on top of the crushed stone layer S, with the bottom surface being the position of the mark 32a on the side portion 32. However, depending on the ground conditions, etc., the structure need not include the crushed stone layer S.

[0035] The pile cap 2 is constructed on the upper surface of the leveling concrete layer C. A plurality of upper end reinforcements 22 are arranged horizontally at predetermined positions a predetermined height below the top surface of the pile cap 2. Also, a plurality of lower end reinforcements 23 are arranged horizontally at predetermined positions a predetermined height above the bottom surface (the upper surface 31 of the formwork 3). Reference numeral 24 denotes stirrups arranged around the upper end reinforcements 22 and the lower end reinforcements 23.

[0036] The cage-shaped restraining reinforcement 40 is provided so as to surround the upper part of the top surface 31 and the side surface 32 of the formwork 3. The following vertical reinforcement 41 constituting the cage-shaped restraining reinforcement 40 is spaced a predetermined distance from the top surface 31 and the side surface 32 of the formwork 3 to ensure the covering thickness.

[0037] The cage-shaped restraining reinforcement 40 has a plurality of vertical reinforcements 41 (eight in this embodiment) arranged at regular intervals according to the number of reinforcements, a pair of upper and lower ring members 43 surrounding the vertical reinforcements 41, and spiral reinforcements 42 (closed horizontal reinforcements) arranged between the upper and lower ring members 43 (Figs. 3(a) and (b)). The thin steel ring member 43 is a member that is installed horizontally to ensure the accuracy of the placement of the vertical reinforcement 41, and two mounting holes 43a for U-shaped bolts 46 are provided at each mounting position of the vertical reinforcement 41.

[0038] The vertical reinforcements 41 are set up at predetermined intervals and are attached to the upper and lower ring members 43 in the mounting holes 43a with U-bolts 46 and nuts 47, with the inner side of each vertical reinforcement 41 abutting against the outer side of each ring member 43. Spiral reinforcements 42 are also arranged between the upper and lower ring members 43 at predetermined intervals in the height direction.

[0039] The upper parts of the top surface part 31 and the side parts 32 of the formwork 3 are inserted into the central space surrounded by the vertical reinforcements 41 of the cage-shaped restraining reinforcement 40. The upper end of each vertical reinforcement 41 is arranged near the upper end reinforcement 22, and the lower end is arranged near the bottom surface of the pile cap 2 (below the lower end reinforcement 23), and extends in the vertical direction of the lower end reinforcement 23.

[0040] The vertical spacing between the upper and lower ring members 43 must be set within the range of reinforcement by the spiral reinforcement 42 (preferably within a range of ±10 cm from the head of the precast pile 1). The spiral reinforcement 42 is attached with binding wires 48 at the points where it intersects with each vertical reinforcement 41.

[0041] (Action and effect) According to this foundation structure K, the presence of formwork 3 covering the head of the precast pile 1 creates a gap E around the head of the pile, which allows the pile head to rotate during an earthquake, etc., and has the effect of preventing a large bending moment from occurring at the head of the pile even if a horizontal force Q (shear force) acting on the structure acts on the precast pile 1 (Figure 1(b)).

[0042] Furthermore, according to this foundation structure K, basket-shaped restraining reinforcement 40 is provided in the pile cap 2 so as to surround the upper surface of the formwork 3, and the upper ends of the vertical reinforcement 41 are arranged near the upper end reinforcement 22 and below the lower end reinforcement 23, thereby effectively preventing shear failure that occurs near the recess 21 in the pile cap 2 during an earthquake, etc.

[0043] (Variation) The foundation structure K of the above embodiment can be suitably used when no pull-out force acts on the prefabricated piles 1. On the other hand, when a pull-out force acts on the precast pile 1, it is possible to effectively cope with the pull-out force by adopting a structure in which a predetermined number of pull-out resistance rods 14 are provided in the pile cap 2' in the vertical direction so that the rods have approximately the same length as the vertical reinforcement 41 (hereinafter referred to as the "modified foundation structure K'"). The pull-out resistance rods 14 are inserted into circular holes 31b provided in the upper surface 31 of the formwork 3 and fixed to the end plates 12 of the precast pile 1 (Figure 4).

[0044] The other structures of the modified basic structure K' are almost the same as those of the basic structure K, and the same effects as those of the basic structure K can be achieved. The pull-out resistance rods 14 can be made of, for example, PC steel rods or structural rolled steel bars (SNR), but the number and strength of the rods should be set to an extent that a semi-rigid connection can be maintained, and there are no restrictions on the method of attachment to the end plates 12.

[0045] [This construction method] Next, the construction method of this embodiment will be described in detail. This construction method consists of the following processes: (1) prefabricated pile installation, (2) formwork installation, (3) leveling concrete installation, (4) reinforcing bars arrangement, and (5) structure foundation concrete installation.

[0046] (1) Prefabricated pile installation process The prefabricated pile driving process is a process of driving a prefabricated pile into the ground G. In this embodiment, a prefabricated pile 1 having a jig 13 that engages with a rotary driving device protruding from the pile head is driven into the ground G using a rotary driving device (not shown).

[0047] The jig 13 engages with the drive shaft of the rotary pressing device and is provided to prevent twisting of the prefabricated pile 1 during rotary pressing. It is made of steel material with an inverted L shape and is fixed to the end plate 12 by welding (Figure 2(a)). The jig 13 may be detachably fixed to the end plate 12 using a mechanical joining method. In addition, when the main body 11 of the precast pile 1 is formed of steel pipe or concrete with an outer steel pipe, the jig 13 may be fixed to the side of the upper end of the main body 11 by welding or the like.

[0048] In this process, a rotary press-in device is used to drive the prefabricated pile 1 into the ground G (Fig. 5(a)). In addition, to prevent soil and sand from clogging the female screw hole 12a of the end plate 12 when the prefabricated pile 1 is rotary pressed in, a bolt B1 is screwed into the female screw hole 12a in advance.

[0049] After the precast pile 1 is driven, the surrounding ground G is excavated to expose the pile head (Fig. 5(b)). Then, the base of the jig 13 attached to the end plate 12 of the precast pile 1 is removed by an appropriate method, such as by melting it down, and the cross section is polished with a grinder or the like to smooth the top surface of the precast pile 1, and the bolt B1 threaded into the female threaded hole 12a is removed (Fig. 5(c)).

[0050] Furthermore, before and after removing the jig 13, any unevenness in the bed surface G1 is leveled, and then crushed stones are laid and compacted on the bed surface G1 to form a crushed stone layer S. In addition, if the crushed stone layer S is not provided due to ground conditions, etc., the process of forming the crushed stone layer S is omitted.

[0051] (2) Formwork installation process The formwork installation process is a process in which the formwork 3 is placed over the head of the precast pile 1, forming a gap E that expands downward between the side of the head of the pile and the inner surface of the side 32 of the formwork 3, and placing ground material S' around the outer periphery of the lower end of the formwork 3.

[0052] In this process, the formwork 3 is placed over the head of the precast pile 1 with the upper surface 31 of the formwork 3 in close contact with the upper end surface of the precast pile 1, and a gap E is formed between the side surface 11a of the head of the pile and the inner surface of the side portion 32 of the formwork 3, the diameter of which increases as it extends downward. When covering the end plate 12 of the pile head with the formwork 3, it is necessary to align the positions of the through hole 31a of the formwork 3 and the female screw hole 12a of the end plate 12 in advance (Figures 2(a) and (b)).

[0053] Next, the pile head of the prefabricated pile 1 is covered with the formwork 3, and then the formwork 3 is temporarily fixed to the pile head using a bolt (fixing tool) B2 that is screwed into the female screw hole 12a. In addition, without providing the female screw hole 12a in the end plate 12, the formwork 3 can be fixed to the pile head by adhesive bonding, welding, etc., with a strength that does not reduce the rotation performance of the pile head.

[0054] After the formwork 3 is temporarily fixed to the head of the precast pile 1, the gap between the lower edge of the formwork 3 and the top surface of the crushed stone layer S is closed by piling up ground material S' around the outer periphery of the lower end of the formwork 3 using the mark 32a on the outer surface as a guide (Figure 6(a)).

[0055] Depending on the site conditions, the lower end of the formwork 3 can be embedded in the crushed stone layer S (corresponding to the ground material S') up to the position of the marker 32a, thereby placing the ground material S' around the lower end of the formwork 3 and the outer periphery of the flange portion 32b (not shown). Alternatively, this can be achieved by digging down the floor surface G1 of the ground G and then placing ground material S' such as crushed stone or soil around its periphery (Figure 7 shows another embodiment of this process), or by burying the lower end and flange 32b of the formwork 3 in the ground G and then forming a crushed stone layer S (corresponding to ground material S') on the floor surface G1 (Figure 4).

[0056] In this embodiment, the head of the precast pile 1 is covered with the formwork 3 before the crushed stone layer S is formed, but the head of the precast pile 1 may also be covered with the formwork 3 after the crushed stone layer S is formed. In addition, in this embodiment, the formwork 3 is fixed to the pile head using the bolts B2 before the ground material S' is banked around the periphery of the formwork 3, but it may also be fixed after the ground material S' is banked.

[0057] (3) Leveling concrete pouring process The concrete pouring process is a process in which leveling concrete is poured around the formwork 3.

[0058] In this step, after placing the ground material S' on the outer periphery of the lower end of the formwork 3, leveling concrete is poured around the formwork 3 to form a leveling concrete layer C (Fig. 6(b)). Although there is no limit to the thickness of the leveling concrete layer C, it is preferable to set the height from the top surface of the leveling concrete layer C to the top surface of the formwork 3 to 5 cm or more.

[0059] After the leveling concrete has hardened, remove the bolts B2. At this time, hit the top surface 31 of the formwork 3 with a mallet or the like to check again that the top surface 31 is in close contact with the top end surface of the precast pile 1, and also hit the side surface 32 with a mallet or the like to check that the leveling concrete has not flowed into the gap E.

[0060] (4) Restraint reinforcement process The restraining bar arrangement process is a process in which the various reinforcing bars (reinforcing bars necessary for foundations such as mats and footings, including upper end bars 22, lower end bars 23 and stirrups 24) to be installed in the pile cap 2 are arranged, and pre-fabricated cage-shaped restraining bars 40 are arranged so as to surround the upper surface of the formwork 3 (Figure 8(a)).

[0061] In this step, in addition to the above-mentioned rebars, cage-shaped restraining reinforcement bars 40 (see the explanation for this foundation structure K) are arranged. At this time, the upper parts of the top surface 31 and side surfaces 32 of the formwork 3 are inserted into the central space surrounded by the vertical reinforcements 41 of the cage-shaped restraining reinforcement bars 40, and the cage-shaped restraining reinforcement bars 40 are installed so as to surround the formwork 3. Furthermore, the vertical reinforcement bars 41 must be spaced so as to ensure a predetermined distance between the top surface 31 and side surfaces 32 of the formwork 3, and the upper ends of the vertical reinforcement bars 41 must be arranged near the upper end reinforcement bars 22 and the lower ends must be arranged near the top surface of the concrete layer C (the bottom surface of the pile cap 2) (below the lower end reinforcement bars 23), so that the vertical reinforcement bars 41 extend in the vertical direction of the lower end reinforcement bars 23. In addition, spacers (not shown) must be interposed between the formwork 3 and the cage-shaped restraint bars 40 in at least three locations in the vertical and horizontal directions, and the cage-shaped restraint bars 40 must be arranged so that they are evenly spaced around the formwork 3.

[0062] (5) Structure foundation concrete pouring process The structure foundation concrete pouring process is a process in which, while the formwork 3 is restrained by the hardened leveled concrete layer C, foundation concrete that will become the pile cap 2 is poured on top of the leveled concrete layer C, and the pile cap 2 is constructed.

[0063] In this process, the reinforcing bars and formwork (not shown) of the pile cap 2 are installed on top of the leveling concrete layer C, and the foundation concrete is poured on top of the leveling concrete layer C and allowed to harden, thereby completing the construction of the foundation structure K (Figure 8(b)).

[0064] (Action and effect) According to this construction method, a constraining reinforcement step is included in which prefabricated cage-shaped constraining reinforcement 40 is arranged to surround the upper surface 31 and the upper part of the side portion 32 of the formwork 3, so that the foundation structure K that can prevent shear failure can be easily constructed. In addition, the formwork 3 used in the formwork installation process is truncated cone shaped and has a flange portion 32b formed on the lower edge, making it easy to handle during construction, which helps to ensure safety during construction. Furthermore, when pouring concrete into the pile cap 2, the formwork 3 is less likely to shift or deform, effectively preventing the concrete and ground material S' from entering the gap E. The ground material S' placed around the bottom end (brim) of the formwork 3 seals the periphery of the bottom end of the formwork 3, preventing the leveling concrete from flowing into the gap E.

[0065] Furthermore, by adopting this construction method, it is possible to realize a semi-rigid connection between the precast pile 1 and the pile cap 2 as envisioned at the time of design. In other words, because the jig 13 for the rotary press-in device attached to the precast pile 1 is removed before the formwork 3 is placed over the pile head of the precast pile 1, it is possible to eliminate the problem of the jig 13 restricting the rotation of the pile head. Furthermore, since the formwork 3 can be restrained by the leveling concrete layer C, the formwork 3 is less likely to shift or deform when the concrete of the pile cap 2 is poured, and furthermore, it is possible to prevent the foundation concrete from seeping into the gap E around the pile head formed by the formwork 3.

[0066] Furthermore, because bolts B2 are used to fix formwork 3 to the head of precast pile 1 before the leveling concrete is poured, it is possible to reliably prevent minute shifts in formwork 3 that may occur when the leveling concrete is poured, and as a result, it is possible to more reliably achieve the joint condition envisioned in the design. Furthermore, because bolts B2 are removed before the foundation concrete is poured, the rotation of the pile head is not restricted, and freedom of rotation is ensured.

[0067] The above describes one example of a preferred embodiment of the present invention, but the present invention is not limited to this embodiment, and appropriate design changes can be made to each element within the scope of the present invention. There are no restrictions on the form of precast piles and structural foundations, or on the construction location of the present invention, and the most suitable components can be adopted for each component of the present invention. Furthermore, the above-mentioned invention-specific matters specify the minimum necessary components, and other components may be added as long as they do not impede the effects of the invention. [Explanation of symbols]

[0068] K,K' Basic structure G Ground S' Ground material S Crushed stone layer C. Leveled concrete layer E gap 1 Prefabricated piles 2 Pile Cap 3 Formwork 11 Main body 21 Recess 22 Top bar 23 Lower end reinforcement 24 Stirrups 31 Top part 32 Side 32a Landmark 32b Tsuba 40 Constrictor cage muscle 41 Vertical muscles 42 Spiral Muscle 43 Ring member

Claims

1. A method for constructing a foundation structure in which a reinforced concrete structure foundation is placed on the heads of precast piles installed in the ground, A prefabricated pile driving process of driving the prefabricated pile into the ground; a formwork installation process in which a frustum-shaped formwork having a flange formed on the periphery is placed over the pile head to form a gap between the side surface of the pile head and the inner peripheral surface of the formwork; A leveling concrete pouring process of pouring leveling concrete around the formwork; A method for constructing a foundation structure, comprising: a structure foundation concrete pouring step of pouring foundation concrete for the structure foundation on the leveling concrete while the formwork is constrained by the leveling concrete.

2. 2. The method for constructing a foundation structure according to claim 1, wherein in the formwork installation step, the formwork covers the pile heads of the prefabricated piles, and then the formwork is temporarily fixed to the pile heads.

3. In the prefabricated pile driving step, a crushed stone layer is formed on the ground, A method for constructing a foundation structure as described in claim 2, characterized in that in the formwork installation process, after the formwork is temporarily fixed to the pile head, ground material is placed around the outer periphery of the lower end portion to close the gap that exists between the lower edge of the formwork and the upper surface of the crushed stone layer.

4. A reinforced concrete structural foundation with a recess on the underside, A foundation structure placed on the pile head of a prefabricated pile driven into the ground in the recess, The recess is formed to widen downward, A foundation structure comprising a formwork having a flange on its periphery, the formwork being integrally formed in the recess.

5. The formwork comprises a disk-shaped upper surface portion and a side portion provided on an outer periphery of the upper surface portion, the inner diameter of which gradually increases downward; The base structure according to claim 4 , wherein the flange is formed on the periphery of the lower surface of the side portion.

6. 6. The base structure according to claim 5, wherein the outer peripheral surface of the side portion has a marking along its lower edge.

7. A crushed stone layer is formed on the ground, A foundation structure as described in claim 4, characterized in that the gap between the lower edge of the formwork and the upper surface of the crushed stone layer is blocked by ground material placed on the outer periphery of the lower end of the formwork.

8. 8. The foundation structure according to claim 7, wherein a layer of leveling concrete is provided around the formwork above the crushed stone layer.

9. A cage-shaped restraining bar is provided so as to surround the upper surface of the formwork, The restraining reinforcement includes a plurality of vertical reinforcements, The foundation structure according to any one of claims 4 to 8, further comprising horizontal reinforcement surrounding the plurality of vertical reinforcement.

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