JP2023056207A - Foundation structure, and construction method of the same - Google Patents

Abstract

To provide a construction method of a foundation structure capable of preventing shear fracture in a joint portion of a precast pile and a foundation structure of semi-rigid connection form.SOLUTION: A construction method of a foundation structure includes: a precast pile installing step; a formwork installing step of covering a pile head portion of the precast pile 1 with a formwork 3 to form a gap E between a side face of the pile head portion and an inner peripheral face of the formwork 3; a leveled concrete installing step of installing leveled concrete around the formwork 3; a restraining bar arranging step of arranging a cage-shaped restraining bar 40 so as to surround an upper face of the formwork 3; and a structure foundation concrete installing step of installing foundation concrete of a structure foundation (a pile cap 2) in a state where the formwork 3 is restrained by the leveled concrete.SELECTED DRAWING: Figure 1

Description

Patent Law Article 30, Paragraph 2 Application Applied Appraisal Application Date: May 14, 2021, Date of Publication (Assessment Date): July 9, 2021, Publication Location (Website Address) https:// www. bcj. or. jp/db/, Published by The Building Center of Japan, Released contents "Evaluation report (construction method, etc.) (BCJ evaluation-FD0141-06), The Building Center of Japan, July 9, 2021" [Published] Items, etc.] Posting date of the website: July 9, 2021, Website address: http://www. ftppile. jp/working_rooms/shiryo. htm, publisher F. T. Pile Construction Method Prefabricated Pile Association, Released Contents “Rating Report (Construction Method, etc.) (BCJ Evaluation-FD0141-06), The Building Center of Japan, July 9, 2021”

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foundation structure in which a structure foundation is placed on the pile heads of ready-made piles installed in the ground, and a construction method thereof.

A so-called semi-rigid joint type foundation structure that can reduce the bending moment generated at the pile head while ensuring high shear force transmission capacity during an earthquake (structural foundation is placed on the pile head of prefabricated piles installed in the ground). Aoshima et al., one of the inventors of the present invention, developed the following construction method. That is, the construction method of this semi-rigid joint structure includes the steps of burying a prefabricated pile having a jig that engages with a rotary press-in device protruding from the pile head portion in the ground using the rotary press-in device, and the jig. A step of removing tools and a form with an inclined inner peripheral surface covering the pile head to form a gap expanding downward between the side surface of the pile head and the inner peripheral surface of the form. placing leveling concrete around the formwork; and placing foundation concrete to serve as a structure foundation on the hardened leveling concrete. (Patent Document 1).

Japanese Patent Application Laid-Open No. 2007-23602

However, in the foundation structure constructed by the conventional construction method, when a horizontal force acts during an earthquake or strong wind (hereinafter referred to as "earthquake etc."), the prefabricated piles on the lower surface of the structure foundation Shear failure occurs at the joint with the head, and there is a possibility of punch-out shear failure due to localized concentrated load.

The present invention was made to solve the above problems, and on the premise of a semi-rigid joint type foundation structure, shear failure occurs at the joint between the prefabricated pile and the pile head on the bottom surface of the structure foundation. It is an object of the present invention to provide a foundation structure and a method of constructing the same that can prevent this.

In order to solve the above problems, the present invention provides a foundation structure in which a reinforced concrete structure foundation having a recess on the bottom surface is placed on the pile head of a prefabricated pile driven into the ground in the recess. The recess is formed to be wider downward, and is provided with a mold having a flange on the peripheral edge, which is integrally provided in the recess, and surrounds the upper surface of the mold. , a cage-shaped restraining muscle is provided, the restraining muscle includes a plurality of vertical muscles, and a horizontal muscle surrounding the plurality of vertical muscles, and each of the vertical muscles is attached to the structure Provided is a foundation structure (hereinafter referred to as "this foundation structure") characterized in that the bottom reinforcements of the lowest part of the foundation are arranged so as to extend in the vertical direction.

Here, “placement” refers to a method of constructing a foundation structure in which a structure foundation (regardless of the shape and type of the structure foundation) is placed on the head of a prefabricated pile that has been driven (buried) into the ground. A semi-rigid joint state in which the structural foundation is simply placed on top of the pile heads of prefabricated piles to support the structural foundation, and the degree of fixation of the joint is reduced to allow rotation. means to be in
The explanation of each term including the above is common to this basic structure and the construction method of this basic structure below.

In addition, the mold has a frustum shape (a shape that slopes so that the inner peripheral surface becomes wider downward), and a flange is formed on the peripheral edge (lower edge) of the lower surface, It is necessary to have a space in Further, the formwork is formed in a truncated cone shape having an upper surface, an open bottom surface having an inner space, and a flange formed at the edge of the circumferential surface of the bottom surface. preferred. There are no restrictions on the size and material of the formwork (including the collar), but if it is made of metal such as steel so that it can withstand the lateral pressure of the concrete, it is preferable because it can prevent damage. is.

In addition, the restraining muscles are provided to resist the shear force generated in the vicinity of the concave portion of the structure foundation (near the pile head joint) when a horizontal force acts. Therefore, it is necessary to provide it appropriately so as to surround the vicinity of the upper surface of the mold. Therefore, in order to achieve the above effects, it is necessary to arrange vertical bars (fixing bars provided in the vertical direction) and horizontal bars (horizontal reinforcing bars provided in the horizontal direction). , weight, installation mode, etc. can be determined appropriately.
The horizontal reinforcing bars are horizontal reinforcing bars formed by bending reinforcing bars into a closed shape, and it is preferable to use helical spiral bars, a plurality of ring-shaped belt bars, or the like.

In addition, the lowermost reinforcement in the structure foundation is the lowest reinforcement in the height direction when there are multiple reinforcing bars that constitute the bottom reinforcement arranged in the structure foundation. means rebar.
Regarding the arrangement of vertical reinforcement, "the reinforcement is arranged so as to extend vertically from the bottom reinforcement at the bottom of the structure foundation" means that the upper end of the vertical reinforcement is the top of the bottom reinforcement at the bottom of the structure foundation. It means that the reinforcement is arranged at the upper position and the lower end of the vertical muscle is arranged at the lower position of the bottom reinforcement of the lowest part.

According to this construction structure, cage-like restraining muscles are formed so as to surround the upper surface of the formwork in the structure foundation, and each vertical muscle that constitutes the restraining muscles is located at the bottom of the structure foundation. Since the bottom reinforcement is arranged to extend vertically, it is possible to effectively prevent shear failure that occurs in the vicinity of the recessed portion of the structure foundation (near the pile head joint) in the event of an earthquake, etc. .

Further, the present invention provides a method for constructing a foundation structure in which a reinforced concrete structure foundation is placed on the pile head of a prefabricated pile provided in the ground, in which the prefabricated pile is driven into the ground. A process and a frustum-shaped formwork with a flange formed on the periphery (hereinafter, the formwork with a flange formed may be referred to as a "formwork with a flange") to the pile head. Formwork installation step of covering and forming a gap between the side surface of the pile head and the inner peripheral surface of the formwork, and leveling concrete placing step of placing leveling concrete around the formwork. a step of arranging a cage-shaped restraining bar so as to surround the upper surface of the formwork; and a step of placing foundation concrete for the structure foundation (hereinafter referred to as "this construction method"). be.

Further, in this construction method, the restraining muscles include a plurality of vertical muscles and horizontal muscles surrounding the plurality of vertical muscles, and each of the vertical muscles is positioned at the lower end of the lowest part of the structure foundation. By arranging the reinforcing bars so as to extend in the vertical direction, it is possible to improve the workability, which is preferable.

Here, the ground material is a general term for crushed stone (pebbles), sand, clay, soil used on site, and the like.
In addition, when placing the ground material around the formwork, it is necessary to embank crushed stones around the formwork and bury the lower end of the formwork in the ground (floor attached surface). An appropriate method can be used depending on the situation.

In the prefabricated pile driving process, the method of driving the prefabricated pile into the ground is not limited. is buried in the ground, and before covering the pile head of the prefabricated pile with the formwork, the jig for the rotary press-in device provided on the prefabricated pile can be removed to prevent noise during construction. In addition, it is possible to eliminate the problem that the rotation of the pile head of the ready-made pile after driving is restrained by the jig.

According to this construction method, since it includes a restraining reinforcement reinforcing process for arranging cage-shaped restraining reinforcements so as to surround the upper surface of the formwork, this foundation structure can prevent shear failure. can be easily constructed.
In addition, the formwork used in the formwork installation process has a truncated cone shape, and since a flange is formed on the periphery of the lower surface, it is easy to handle during construction, contributing to ensuring safety during construction. become.

Furthermore, since the formwork with brim is used to place the leveled concrete, the presence of the brim prevents the formwork from slipping or deforming when pouring the concrete for the structure foundation, thereby preventing gaps from forming. It can effectively prevent the intrusion of concrete and ground materials.

In this construction method, before the leveling concrete placing step, the formwork is fixed to the pile head using a fixing device, and before the foundation concrete placing step, the fixing device is fixed. If it is removed, it is possible to reliably prevent the formwork from being slightly misaligned when pouring leveled concrete, so it is possible to more reliably obtain the joint state as assumed at the time of design. It is preferable because it can

In addition, in this construction method, a mark is marked along the lower edge of the outer peripheral surface of the formwork, and before the step of placing leveled concrete, the outer periphery of the lower end of the formwork is marked with: By arranging the ground material or leveling concrete up to the position of the above mark, it is possible to improve convenience during construction, and it is formed between the side surface of the pile head and the inner peripheral surface of the formwork. Since it is possible to prevent concrete from flowing into the gap, it is possible to reliably secure the gap around the pile head, which is preferable.

Advantageous Effects of Invention According to the present invention, it is possible to provide a foundation structure and a method of constructing the same that can prevent shear failure at the joint between a prefabricated pile of a semi-rigid joint type and a foundation structure.

BRIEF DESCRIPTION OF THE DRAWINGS It is a sectional side view which shows the foundation structure of this invention, (a) is normal time, (b) is each shown at the time of an earthquake. (a) is a perspective view showing a ready-made pile used in the foundation structure of the present invention, and (b) is a perspective view showing a formwork used in the foundation structure of the present invention. (a) is a perspective view showing a cage-like restraint muscle used in the foundation structure of the present invention, and (b) is an enlarged view of the X portion of FIG. 3(a). FIG. 4 is a side cross-sectional view showing another embodiment of the foundation structure of the present invention; (a) to (c) are side cross-sectional views for explaining a prefabricated pile driving step in the construction method of the foundation structure of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a sectional side view for demonstrating the construction method of the foundation structure of this invention, Comprising: (a) shows a form installation process, (b) shows a leveling concrete placing process, respectively. FIG. 4 is a side cross-sectional view showing another embodiment of the formwork installation step in the construction method of the foundation structure of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a sectional side view for demonstrating the construction method of the foundation structure of this invention, Comprising: (a) shows a restraint reinforcement reinforcement process, (b) shows a structure foundation concrete casting process, respectively.

An example of an embodiment of this basic structure and this construction method will be described in detail below with reference to the drawings. In the description based on the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. Also, in FIGS. 1(a), 1(b), 4, 8(a) and 8(b), the cage-like restraint muscles 40 are shown in a simplified form for the sake of drawing.

[This basic structure]
First, before explaining this construction method, this 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 capability. It is a structure that is placed on the pile head of the ready-made pile 1 that has been driven (Fig. 1(a)).

(Prefabricated pile)
The prefabricated pile 1 includes 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, PC steel bars (not shown) are arranged in the longitudinal direction (vertical direction) of the main body 11 .
The main body 11 may be made of any material as long as it can obtain a predetermined strength. can.

The end plate 12 is made of steel, and is fixed to the upper end surface of the body portion 11 by embedding an anchor (not shown) projecting from the bottom surface of the body portion 11 . In addition, a plurality of female screw holes 12a are formed in the end plate 12 at predetermined intervals in the circumferential direction (in FIG. 2(a), the jig 13 used in the ready-made pile driving process of this construction method is shown). is being used).
When the main body 11 is made of steel, the end plates 12 are usually fixed by welding, but depending on the situation, the end plates 12 may be omitted.

(pile cap)
The pile cap 2 is a structure made of reinforced concrete, and has a frustum-shaped concave portion 21 (a concave portion widened toward the bottom) formed on the bottom surface thereof. That is, in a state in which the pile head of the prefabricated pile 1 is covered with the formwork 3, the foundation concrete that becomes the pile cap 2 is placed. With the above configuration, the formwork 3 and the foundation concrete are integrated, and the recess 21 having the same shape as the space of the formwork 3 is formed.

The formwork 3 has a disk-shaped upper surface portion 31 that abuts on the upper end surface of the prefabricated pile 1 (the upper surface of the end plate 12) whose inner peripheral surface is inclined, and a side portion 32 that surrounds the pile head portion of the prefabricated pile 1. It has a truncated conical appearance (Fig. 2(b)).

The upper surface portion 31 has the same planar shape as the upper end surface of the pile head portion of the prefabricated pile 1 . Through holes 31a for temporarily fixing the end plate 12 are formed in the upper surface portion 31 at a plurality of positions (two positions in the present embodiment) corresponding to the female screw holes 12a of the end plate 12. .
The side portion 32 is provided on the outer peripheral edge of the upper surface portion 31, the inner diameter thereof gradually increases downward, and a collar portion 32b is formed on the peripheral edge of the lower surface.

Furthermore, marks 32 a are marked along the lower edge of the formwork 3 on the outer peripheral surface of the side portion 32 to serve as a guide when embedding the side portion 32 in the crushed stone layer S.
The mark 32a is preferably formed at a position at least 2 cm above the lower edge of the mold 3. As shown in FIG. Further, in the present embodiment, the mark 32a is written continuously over the entire circumference of the side portion 32, but the mark 32a is not limited to this, and may be written intermittently.

The pile head of the prefabricated pile 1 is arranged in contact with the inner surface of the upper surface portion 31 of the formwork 3, and the presence of the formwork 3 creates a gap around the pile head of the prefabricated pile 1. E is formed.

Further, a crushed stone layer S of a predetermined thickness is formed on the ground G, and above the crushed stone layer S is a leveled concrete layer C of a predetermined thickness whose bottom surface is the position of the mark 32a of the side portion 32. is provided. However, depending on the ground conditions, etc., the crushed stone layer S may not be provided.

The pile cap 2 is constructed on the upper surface of the leveled concrete layer C. In the pile cap 2, a plurality of top reinforcements 22 are arranged in the horizontal direction at predetermined positions below the upper surface by a predetermined height. In addition, a plurality of bottom reinforcements 23 are arranged in the horizontal direction at predetermined positions above the bottom surface (upper surface portion 31 of the formwork 3) by a predetermined height. Reference numeral 24 denotes stirrups provided around the upper muscle 22 and the lower muscle 23 .

Moreover, the cage-like restraint bar 40 is provided so as to surround the upper portions of the upper surface portion 31 and the side portions 32 of the formwork 3 . Each vertical muscle 41 that constitutes the cage-shaped restraining muscle 40 is spaced from the upper surface 31 and the side 32 of the formwork 3 by a predetermined distance, so that the covering thickness is ensured.

The cage-shaped restraining muscles 40 are composed of a plurality of vertical muscles 41 (eight in this embodiment) provided at regular intervals according to the number of the restraining muscles 40, and a pair of upper and lower muscles surrounding the plurality of vertical muscles 41. and spiral ribs 42 (closed horizontal ribs) provided between the upper and lower ring members 43 (FIGS. 3(a) and 3(b)).
The steel thin plate-shaped ring member 43 is a member provided in the horizontal direction to ensure the placement accuracy of the vertical bars 41, and two mounting holes 43a for U-shaped bolts 46 are provided at each mounting position of the vertical bars 41. is provided.

Each vertical muscle 41 erected at a predetermined interval is attached to a U-shaped bolt 46 and a nut 47 in the mounting hole 43 a in a state in which the inner side surface of each vertical muscle 41 is in contact with the outer side surface of each ring member 43 . are attached to the upper and lower ring members 43 by In addition, between the upper and lower ring members 43, spiral reinforcements 42 are arranged at predetermined intervals in the height direction.

The upper portions of the upper surface portion 31 and the side portions 32 of the formwork 3 are inserted into the central space surrounded by the vertical muscles 41 of the cage-shaped restraining muscles 40 . Each vertical muscle 41 has an upper end arranged near the upper reinforcement 22 and a lower end arranged near the bottom surface of the pile cap 2 (below the lower reinforcement 23). extends vertically.

The vertical interval 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 pile head of the ready-made pile 1). Moreover, the spiral muscle 42 is attached with a binding wire 48 at the point where it intersects with each vertical muscle 41 .

(Effect)
According to this foundation structure K, due to the presence of the formwork 3 covering the pile head of the prefabricated pile 1, there is a gap E around the pile head. is allowed to rotate, and even if the horizontal force Q (shear force) acting on the structure acts on the prefabricated pile 1, a large bending moment is not generated at the pile head. (Fig. 1(b)).

In addition, according to this construction structure K, the cage-like restraining muscles 40 are provided so as to surround the upper surface of the formwork 3 in the pile cap 2 , and the vertical muscles 41 have upper ends near the upper end muscles 22 . , and the lower end portion is arranged below the lower end reinforcement 23, it is possible to effectively prevent shear failure occurring in the vicinity of the recess 21 in the pile cap 2 during an earthquake or the like.

(Modification)
The foundation structure K of the above embodiment can be suitably used when no pulling force acts on the prefabricated pile 1 .
On the other hand, when a pull-out force acts on the ready-made pile 1, a structure in which a predetermined number of pull-out resistance rods 14 are provided in the vertical direction so as to have substantially the same length as the vertical reinforcement 41 is adopted in the pile cap 2'. Thereby, it becomes possible to effectively cope with the pull-out force (hereinafter referred to as "this basic structure K' of the modified example"). The pull-out resistance rod 14 is inserted through a circular hole 31b provided in the upper surface portion 31 of the formwork 3 and fixed to the end plate 12 of the ready-made pile 1 (Fig. 4).

Other structures in this basic structure K' of a modification are substantially the same as that of the said basic structure K, and the effect similar to this basic structure K can be exhibited.
For the pull-out resistance rods 14, for example, PC steel rods or rolled steel bars for construction structures (SNR) can be used, but the number and strength thereof are set to such an extent that a semi-rigid joint state can be maintained. There is no limitation on the mounting method to the fixing plate 15 .

[This construction method]
Next, the construction method of this embodiment will be described in detail.
This construction method includes (1) a ready-made pile driving process, (2) a form setting process, (3) a leveling concrete driving process, (4) a restraining bar reinforcement process, and (5) a structure It is composed of a process including a foundation concrete placing process.

(1) Ready-made pile driving process The ready-made pile driving process is a process of driving a ready-made pile into the ground G. In the present embodiment, the jig 13 engaged with the rotary press-fitting device A ready-made pile 1 projecting from the ground is driven into the ground G using a rotary press-fitting device (not shown).

The jig 13 engages with the drive shaft of the rotary press-fitting device and is provided to prevent the prefabricated pile 1 from twisting during rotary press-fitting, and is made of a steel material having an inverted L shape. , are fixed to the end plate 12 by welding (FIG. 2(a)).
Alternatively, the jig 13 may be detachably fixed to the end plate 12 using a mechanical joining method. When the main body 11 of the prefabricated pile 1 is made of a steel pipe or concrete with an outer shell steel pipe, the side surface of the upper end of the main body 11 may be fixed by welding or the like.

In this step, a ready-made pile 1 is driven into the ground G using a rotary press-in device (Fig. 5(a)). A bolt B1 is screwed into the female screw hole 12a in advance so that the female screw hole 12a of the end plate 12 is not clogged with sand or the like when the ready-made pile 1 is rotationally press-fitted.

After driving the ready-made pile 1, the surrounding ground G is dug down to expose the pile head (Fig. 5(b)). Then, the base of the jig 13 attached to the end plate 12 of the prefabricated pile 1 is removed by an appropriate method such as fusion cutting, and the cross section is polished with a grinder or the like to smooth the upper end surface of the prefabricated pile 1. , remove the bolt B1 screwed into the female screw hole 12a (FIG. 5(c)).

Furthermore, before and after removing the jig 13, the unevenness of the floor surface G1 is adjusted, and crushed stone is laid and rolled on the floor surface G1 to form a crushed stone layer S.
If the crushed stone layer S is not provided due to ground conditions or the like, the step of forming the crushed stone layer S is omitted.

(2) Formwork installation process In the formwork installation process, the formwork 3 is covered over the pile head of the ready-made pile 1, and the side surface of the pile head and the inner peripheral surface of the side part 32 of the formwork 3 In this step, a gap E that expands downward is formed in the mold 3, and a ground material S' is placed around the outer periphery of the lower end of the mold 3.

In this step, the formwork 3 is covered over the pile head of the prefabricated pile 1 while the upper surface portion 31 of the formwork 3 is in close contact with the upper end surface of the prefabricated pile 1, and the side surface 11a of the pile head and the form Between the frame 3 and the inner peripheral surface of the side portion 32, a gap E whose diameter increases downward is formed.
In addition, 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 (Fig. 2 (a), (b)).

Subsequently, after the pile head of the prefabricated pile 1 is covered with the formwork 3, the formwork 3 is temporarily fixed to the pile head using bolts (fasteners) B2 that are screwed into the female screw holes 12a.
Without providing the end plate 12 with the female screw hole 12a, the formwork 3 can be fixed to the pile head by adhesion, welding, or the like with a strength that does not degrade the rotation performance of the pile head.

After temporarily fixing the formwork 3 to the pile head of the prefabricated pile 1, using the mark 32a marked on the outer peripheral surface as a guide, the ground material S' is embanked around the outer periphery of the lower end of the formwork 3, etc. The gap existing between the lower edge of the formwork 3 and the upper surface of the crushed stone layer S is closed (Fig. 6(a)).

Depending on the site conditions, the lower end of the formwork 3 may be embedded in the crushed stone layer S (corresponding to the ground material S′) up to the position of the mark 32a. It is also possible to place a ground material S' in (not shown).
In addition, after excavating the floor surface G1 of the ground G, the ground material S' such as crushed stone and earth and sand is arranged on the outer periphery (Fig. 7 shows another embodiment of this process), or a mold This can be dealt with by embedding the lower end of the frame 3 and the flange 32b in the ground G and then forming a crushed stone layer S (corresponding to the ground material S') on the floor surface G1 (Fig. 4).

In this embodiment, before the crushed stone layer S is formed, the pile heads of the prefabricated piles 1 are covered with the formwork 3. It may cover the pile head.
Further, in this embodiment, the formwork 3 is fixed to the pile head using the bolt B2 before embanking the ground material S' around the outer periphery of the formwork 3, but it is fixed after embanking the ground material S'. may

(3) Leveling Concrete Placement Step The concrete placement step is a step of placing leveling concrete around the formwork 3 .

In this step, after placing the ground material S' on the outer periphery of the lower end of the formwork 3, leveling concrete is placed around the formwork 3 to form a leveling concrete layer C (Fig. 6 ( b)).
Although the thickness of the leveled concrete layer C is not limited, it is preferable to set the height from the upper surface of the leveled concrete layer C to the upper surface of the formwork 3 to be 5 cm or more.

After the leveling concrete has hardened, the bolt B2 is removed. At this time, the upper surface portion 31 of the formwork 3 is hit with a mallet or the like to reconfirm that the upper surface portion 31 is in close contact with the upper end surface of the prefabricated pile 1, and the side portions 32 are hit with a mallet or the like. , and confirm that no leveling concrete has flowed into the gap E.

(4) Reinforcement Reinforcement Arrangement Process In the reinforcement reinforcement process, various rebars provided in the pile cap 2 (rebars necessary for the foundation of mats, footings, etc., including the upper end bar 22, the lower end bar 23, and the stirrup 24) ), and arranging prefabricated cage-like restraint bars 40 so as to surround the upper surface of the formwork 3 (FIG. 8(a)).

In this step, in addition to the above reinforcing bars, cage-like constraining bars 40 (see the explanation for this basic structure K) are arranged. At this time, the upper portions of the upper surface portion 31 and the side portions 32 of the formwork 3 are inserted into the central space surrounded by the respective vertical muscles 41 of the cage-shaped restraint muscles 40 , and the cage-shaped restraint muscles 40 are inserted into the formwork 3 . be installed so as to surround the In addition, the vertical reinforcement 41 is separated so that a predetermined distance is secured between the upper surface portion 31 and the side portion 32 of the formwork 3, and the upper end portion of the vertical reinforcement 41 is arranged in the vicinity of the upper end reinforcement 22. In addition, the lower end is leveled and the reinforcement is arranged near the upper surface of the concrete layer C (bottom surface of the pile cap 2) (below the bottom reinforcement 23), and the vertical reinforcement 41 extends in the vertical direction of the bottom reinforcement 23. It is necessary to arrange the bar so that
Spacers (not shown) are interposed vertically and horizontally between the formwork 3 and the cage-like restraint bars 40 at at least three locations, so that the cage-like restraint bars 40 are positioned between the formwork 3 and the formwork 3 . should be evenly spaced around the perimeter of the

(5) Structural Foundation Concrete Casting Step In the structural foundation concrete casting step, the formwork 3 is constrained by the hardened leveled concrete layer C, and the foundation that will become the pile cap 2 is placed on the leveled concrete layer C. This is the step of placing concrete and constructing the pile cap 2 .

In this step, the reinforcing bars and formwork (not shown) of the pile cap 2 are placed on the leveled concrete layer C, and the foundation concrete is placed on the leveled concrete layer C and hardened. Construction of this basic structure K is completed (FIG. 8(b)).

(Effect)
According to this construction method, there is provided a restraining reinforcement reinforcement step of arranging the prefabricated cage-shaped restraining reinforcements 40 so as to surround the upper surface portion 31 and the upper portion of the side portion 32 of the formwork 3. Therefore, it is possible to easily construct the basic structure K that can prevent shear failure.
In addition, since the formwork 3 used in the formwork installation process has a truncated cone shape and a brim portion 32b is formed on the lower edge, it is easy to handle during construction. will be invested.
Furthermore, when the concrete for the pile cap 2 is placed, the formwork 3 is less likely to shift and deform, and the intrusion of the concrete and the ground material S' into the gap E can be effectively prevented. Since the periphery of the lower end of the formwork 3 is sealed by the ground material S′ arranged around the lower end (flange) of the formwork 3, the smoothed concrete is prevented from flowing into the gap E. be able to.

Moreover, by adopting this construction method, it is possible to realize a semi-rigid joint state between the prefabricated pile 1 and the pile cap 2 as assumed at the time of design. That is, before the pile head of the prefabricated pile 1 is covered with the formwork 3, the jig 13 for the rotary press-in device provided on the prefabricated pile 1 is removed, so that the rotation of the pile head is restrained by the jig 13. It is possible to eliminate the problem of being
Furthermore, since the formwork 3 can be constrained by the leveled concrete layer C, when the concrete of the pile cap 2 is placed, the formwork 3 is less likely to shift or deform. It is possible to prevent foundation concrete from penetrating into the gap E around the pile head.

In addition, since the formwork 3 is fixed to the pile head of the ready-made pile 1 using the bolt B2 before the leveling concrete is placed, the formwork 3 generated when the leveling concrete is placed. It is possible to reliably prevent minute deviations, and as a result, it is possible to more reliably obtain the bonding state as assumed in the design. Since the bolt B2 is removed before placing the foundation concrete, the rotation of the pile head is not restricted, and the degree of freedom of rotation is ensured.

As described above, an example of a preferred embodiment of the present invention has been described, but the present invention is not limited to this embodiment, and design changes can be made to each element as appropriate without departing from the gist of the present invention.
There are no restrictions on the form of prefabricated piles and structural foundations, and the construction sites of the present invention, and optimum components can be adopted for each component of the present invention. In addition, the above-mentioned matters specifying the invention define the minimum necessary components, and other components may be added as long as they do not interfere with the effects.

K, K' Foundation structure G Ground S' Ground material S Crushed stone layer C Leveled concrete layer E Gap 1 Ready-made pile 2 Pile cap 3 Formwork 11 Main body 21 Recess 22 Top reinforcement 23 Bottom reinforcement 24 Stirrup 31 Upper surface 32 side Part 32a Mark 32b Flange 40 Cage-shaped restraining muscle 41 Vertical muscle 42 Spiral muscle 43 Ring member

Claims (3)

In a method for constructing a foundation structure in which a reinforced concrete structure foundation is placed on the pile head of a prefabricated pile provided in the ground,
a prefabricated pile driving step of driving the prefabricated pile into the ground;
A form that forms a gap between the side surface of the pile head and the inner peripheral surface of the form by covering the pile head with a frustum-shaped form having a flange formed on the peripheral edge. an installation process;
a leveling concrete placing step of placing leveling concrete around the formwork;
a restraining-reinforcement reinforcement step of arranging cage-shaped restraining-reinforcements so as to surround the upper surface of the formwork;
a structure foundation concrete placing step of placing the foundation concrete of the structure foundation on the leveled concrete in a state where the formwork is constrained by the leveled concrete. construction method. The restraining muscles include a plurality of vertical muscles,
a horizontal muscle surrounding the plurality of vertical muscles;
2. The method of constructing a foundation structure according to claim 1, wherein each of said vertical reinforcements is arranged so as to extend vertically from a lowermost bottom reinforcement of said structure foundation. A reinforced concrete structure foundation with a recess on the bottom surface,
A foundation structure placed on the pile head of a prefabricated pile driven into the ground in the recess,
The recess is formed wider downward,
A mold having a flange on the peripheral edge is provided integrally with the recess, and
A cage-shaped restraining muscle is provided so as to surround the upper surface of the formwork,
The restraining muscles include a plurality of vertical muscles,
a horizontal muscle surrounding the plurality of vertical muscles;
The foundation structure, wherein each of the vertical reinforcements is arranged so as to extend vertically from the bottom reinforcement of the lowest part of the structure foundation.

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