Prefabricated concrete pile covered with steel pipe, and foundation pile construction

Abstract

To prevent buckling of a steel pipe against acting tensile stress or bending stress, and to exhibit the maximum tensile resistance even if a steel pipe 20 is closely attached to an outer surface 4 of a prefabricated pile body 1, and horizontal force acts on the prefabricated pile while a compressive load is acting on the prefabricated pile.SOLUTION: The steel pipe 20 is attached to the outer surface 4 of the prefabricated concrete pile body 1 to form a prefabricated pile 50. The prefabricated pile main body 1 is formed in a cylindrical shape, and a reduced diameter portion 10 is formed on the outer surface 4 side of a lower end, an upper end plate 15 with an outer diameter D1 is provided at an upper end 2, and an upper end plate 17 with an outer diameter D2 (<D1) is provided at a lower end 3. An upper end 21 of the steel pipe 20 is fixed to the upper end plate 15, and a lower end 22 of the steel pipe 20 is located near an upper end of the reduced diameter portion 10 of the prefabricated pile main body 1, and the lower end 22 of the steel pipe 20 is not located in the reduced diameter portion 10. The reduced diameter portion 10 has a configuration (a) in which a steep slope 11 and a gentle slope 12 are provided, and a configuration (b) in which the diameter is reduced linearly.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This invention relates to a foundation pile structure comprising a precast concrete pile covered with a steel pipe, which serves as an upper precast pile, and a connected precast pile formed by connecting a lower precast pile to the upper precast pile, which are buried in a pile hole. [Background technology]

[0002] Conventionally, when constructing foundation piles by burying prefabricated piles in pile holes filled with hydraulic material, in addition to compressive vertical loads such as the compressive force of the upper structure and the tensile force due to pulling out, the action of horizontal loads due to earthquakes, etc. must be considered near ground level. Steel pipe piles are sometimes used near ground level to withstand horizontal loads, but to take into account buckling under vertical loads, the thickness of the steel pipes needs to be increased, so in some cases prefabricated concrete piles with steel pipes covering the outer periphery (so-called SC piles) are used. In this case, in order to prevent the steel pipe from bulging outward due to buckling and adversely affecting the compressive force of the concrete pile, for example, a proposal has been made to deal with buckling by providing an additional concrete layer and an outer shell steel pipe on the outside of the steel pipe (Patent Document 1).In addition, in the case of Patent Document 1, not only was it complicated to manufacture such a prefabricated pile, but when connecting other prefabricated piles below, it was necessary to take complicated measures such as standardizing the diameter of the concrete part. In order to eliminate such complicated work, a proposal has been made to form a buffer section by cutting out a steel pipe in a prefabricated concrete pile covered with a steel pipe, thereby effectively dealing with the buckling of the steel pipe, i.e., the compressive force acting on a prefabricated concrete pile covered with a steel pipe, without changing the diameter of the prefabricated concrete pile portion (Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2016-223207 [Patent Document 2] Patent Publication No. 2021-127667 Summary of the Invention [Problem to be solved by the invention]

[0004] In this case, the steel pipe was adequately protected against compressive forces, but it was not adequately protected against elongation of the steel pipe when an unexpected tensile force was applied. [Means for solving the problem]

[0005] This invention solves the above-mentioned problems by using a steel pipe covering a prefabricated pile body in which the upper end of the steel pipe is fixed to an upper end plate but the lower end of the steel pipe is not fixed to a lower end plate.

[0006] In other words, this precast pile invention is a precast concrete pile covered with a steel pipe, characterized in that a steel pipe is arranged around the outer periphery of a precast concrete pile body as follows. (1) An upper pile end plate is provided at the upper end of the precast pile body, and a lower pile end plate is provided at the lower end of the precast pile body. (2) The upper end of the steel pipe was fixed to the upper pile end plate at the upper end of the precast pile body. (3) The lower end of the steel pipe was not fixed to the lower end plate of the precast pile body, and the lower end of the steel pipe was positioned above the lower end plate of the precast pile body.

[0007] In addition, in the prefabricated pile invention, This is a precast concrete pile covered with a steel pipe, characterized in that the inner diameter of the precast pile body is kept the same, the lower end of the outer surface of the precast pile body is reduced in diameter to form a reduced diameter portion, and the outer diameter of the lower end plate is made smaller than that of the upper end plate. The present invention also provides a precast concrete pile covered with a steel pipe, characterized in that it is configured as follows. (1) The lower end of the precast pile body was gradually reduced in diameter to form a reduced diameter section, and the outer diameter of the lower end plate was made smaller than that of the upper end plate. (2) The lower end of the steel pipe was positioned at the same position as the upper end of the reduced diameter portion or higher than the upper end of the reduced diameter portion.

[0008] In addition, the invention of the foundation pile structure is characterized in that a connected precast pile formed by connecting the lower end plate of the upper precast pile made of concrete coated with a steel pipe and having a diameter D2 to the upper end plate of the lower precast pile made of concrete coated or not coated with a steel pipe and having a diameter D1 is buried in a pile hole and configured as follows. (1) The upper precast pile is configured as follows. (a) An upper pile end plate with an outer diameter D1 is provided at the upper end of the precast pile body, a lower pile end plate with a diameter D2 is provided at the lower end of the precast pile body, and a reduced-diameter portion is formed at the lower end portion of the precast pile body, with D2 < D1. (b) The upper end of the steel pipe is fixed to the upper pile end plate of the precast pile body. (c) The lower end of the steel pipe is not fixed to the lower end plate of the precast pile body, and the lower end of the steel pipe is positioned above the lower end plate of the precast pile body. (2) A hydraulic material is filled between the pile hole and the outer periphery of the connected precast pile. (3) The upper precast pile is "positioned near the ground" or "positioned at the uppermost part of the precast pile".

[0009] In addition, in the invention of the foundation pile structure, the described foundation pile structure is characterized in that it is configured as follows. (1) The lower end portion of the connected precast pile body of the upper precast pile is gradually reduced in diameter to form a reduced-diameter portion. (2) The lower end of the steel pipe is positioned at the same level or above the upper end of the reduced-diameter portion.

[0010] In addition, the "precast pile made of concrete (precast pile body)" in the above refers to the so-called general term "made of concrete", which usually uses materials such as concrete and mortar obtained by mixing aggregates and other materials in a hydraulic material such as cement as the main material, and includes precast piles with a structure in which various steel materials, resin materials, etc. are embedded and contained as reinforcing materials.

Effects of the Invention

[0011] This invention A steel pipe covering a precast pile body, with the upper end of the steel pipe fixed to the upper end plate and the lower end of the steel pipe not fixed to the lower end plate. Therefore, even when a horizontal force acts in a state where a compressive load acts on the precast pile, buckling of the steel pipe is prevented against the acting tensile stress and bending stress, and a precast concrete pile covered with a steel pipe that maximally exhibits tensile resistance can be realized. In addition, since the precast pile of the present invention is provided with a lower end plate, it can be connected to a lower precast pile located directly below by ordinary connecting means to form a connected precast pile.

Brief Description of the Drawings

[0012] [Figure 1] (a) is an embodiment of a precast concrete pile covered with a steel pipe, and (b) is another embodiment of a precast concrete pile covered with a steel pipe. [Diagram 2] (a) represents a diagram schematically explaining the manufacture of a precast concrete pile covered with a steel pipe of the present invention, and (b) represents a diagram schematically explaining the manufacture of a conventional concrete-filled steel pipe pile (so-called SC pile). [Diagram 3] A longitudinal sectional view of a connected precast pile in which precast concrete piles covered with a steel pipe of the present invention are connected is shown. [Figure 4] (a) to (e) are longitudinal sectional views explaining the steps of constructing the foundation pile structure of the present invention.

Mode for Carrying Out the Invention

[0013] 1. Configuration of the precast pile 50 made of concrete covered with a steel pipe

[0014] (1) The precast pile body 1 made of concrete is formed in a cylindrical shape, and a reduced-diameter portion 10 is formed on the outer surface 4 side of the lower end portion. An (ordinary) upper end plate 15 made of a donut-shaped steel plate with an inner diameter D0 and an outer diameter D1 is provided at the upper end 2 of the precast pile body 1, and an (ordinary) upper end plate 17 made of a donut-shaped steel plate with an inner diameter D0 and an outer diameter D2 (<D1) is provided at the lower end 3. A steel pipe 20 is in intimate contact with the outer surface 4 of the precast pile main body 1, with the upper end 21 of the steel pipe 20 fixed to the lower surface (or side surface) of the upper end plate 15, and the lower end 22 of the steel pipe 20 located near the upper end of the reduced diameter portion 10 of the precast pile main body 1. Therefore, the entire lower end surface 20a of the steel pipe 20 is exposed facing downward. Therefore, the steel pipe 20 is not arranged in the reduced diameter portion 10 of the precast pile main body 1, and only the outer surface 4 of the precast pile main body 1 is exposed. Furthermore, due to the above structure, the steel pipe 20 is naturally not fixed to the lower end plate 17, and the lower end 22 of the steel pipe 20 is located above the lower end plate 17. Therefore, the entire lower end surface 22a of the steel pipe 20 is exposed downward (Figure 1(a)), but there are also cases (not shown) where the inner periphery of the lower end surface 22a is embedded in the prefabricated pile body 1 (where only the outer periphery of the lower end surface 22a is exposed). In addition, the upper end of the reduced diameter section 10 is formed as a steep slope 11 where the diameter reduces somewhat abruptly from the outer surface 4 of the precast pile body 1, followed by a gentle slope 12 where the diameter gradually reduces toward the lower end to a diameter D2. Moreover, the central opening 16 of the upper end plate 15, the central opening 18 of the lower end plate 17, and the inner surface of the hollow portion 6 of the prefabricated pile body 1 all have the same diameter D0. In this manner, a precast concrete pile 50 covered with a steel pipe is constructed (FIG. 1(a)).

[0015] (2) In this case, reinforcing steel materials such as reinforcing bars may be embedded in the prefabricated pile body 1 (not shown). In the above, the steep slope 11 and the gentle slope 12 are formed in the narrowed diameter portion of the narrowed diameter portion 10, but they may be formed with the same narrowing rate (linear narrowing) (FIG. 1(b)). In this case, the narrowed diameter portion 10 is formed with only the gentle slope 12 having a slightly larger narrowing rate than in the above embodiment.

[0016] 2. Manufacturing of prefabricated piles 50 made of concrete covered with steel pipes

[0017] (1) Conventionally, a precast concrete pile 66 covered with a steel pipe 20 (so-called SC pile) has a steel pipe 62 covering the entire length of a precast pile body 63. An upper end plate 64 and a lower end plate 65 are fixed to the steel pipe 62 and arranged horizontally. The steel pipe 62 and the upper and lower end plates 64, 65 form a formwork (Figure 2(b)), and the pile is attached to an SC pile manufacturing device (not shown). Typically, a holding jig (not shown) is arranged to cover the central opening 64 of the upper end plate 64 and support the upper end plate 64, and similarly, a holding jig (not shown) is arranged to cover the central opening 64 of the upper end plate 64 and support the upper end plate 64. The holding jig can apply the necessary external force to the upper and lower end plates 64, 65 when PC steel bars or reinforcing bars are placed between the upper and lower end plates 64, 65. Then, concrete is filled into the formwork formed by the steel pipe 62 and the upper and lower end plates 64, 65, and the steel pipe 62 is centrifugally formed while rotating in the axial direction to form a prefabricated pile body 63 with a hollow portion 63a inside the steel pipe 64 (Figure 2(b)). After a specified curing period, a prefabricated pile (a concrete pile covered with a steel pipe) 66 is completed.

[0018] (2) In the precast concrete pile 50 covered with this steel pipe 20, since the steel pipe 20 is not located in the reduced diameter portion 10 of the precast pile body 1, a lower formwork jig 31 such as that shown below is used in place of the retaining jig on the lower end plate 17 side in the manufacture (Figure 2(a)). The lower form jig 31 is disposed so as to fix one end (upper end 21 ) of the steel pipe 20 to the upper end plate 15 and to be in close contact with the lower end 22 of the steel pipe 20 . The lower form jig 31 has one end of a support cylinder 34 fixed to a circular support disk 33 to form a jig body 32 with one end open and the other end closed, and a reduced diameter portion forming cylinder 35 that matches the outer circumferential shape of the reduced diameter portion 10 is connected to the open side of the support cylinder 34. The reduced diameter portion forming cylinder 35 is formed with a cylindrical gentle slope forming portion 36 that corresponds to the gentle slope 12, followed by a cylindrical steep slope forming portion 36 that corresponds to the steep slope 11. Furthermore, on the open side of the steep slope forming portion 36, a cylindrical steel pipe locking portion 38 is formed that abuts against the entire end face of the other end face (lower end face 22a) of the steel pipe 20 and locks onto the outer surface side of the other end. In the lower form jig 31, the lower end plate 17 is disposed within the support cylinder 34, and a lower end plate holder 41 is disposed to hold the lower end plate 17 in a predetermined position and close the central opening 18 of the lower end plate 17. The lower end plate holder 41 is attached to the support disk 33 by a size adjustment tool 42 that adjusts the axial position of the lower end plate 17. The size adjustment tool 42 is disposed along the central axial direction of the steel pipe 20.

[0019] (3) The steel pipe 20 and the engaged lower form jig 31 are horizontally mounted on a normal SC pile manufacturing device (not shown) (FIG. 2(a)). The upper end plate 15 is supported by a normal holding jig (not shown). While rotating around its axis, a predetermined amount of concrete for forming the precast pile body 1 is poured into the steel pipe 20 and the lower formwork jig 31, thereby forming a precast pile body 1 with a hollow portion 6 of a predetermined diameter D0, and after a predetermined curing process, a precast pile 50 is formed (Figure 1(a)). When PC steel bars or reinforcing bars (neither shown) are placed inside the precast pile body 1, the lower end plate holder 41 can work in cooperation with the holding jig on the upper end plate 15 side to fix the PC steel bars or reinforcing bars or to tension the PC steel bars.

[0020] (4) Other embodiments (manufacturing method) In the above, the structure of the lower form jig 31 can be any structure (not shown) as long as it can form the reduced diameter portion 10 in the prefabricated pile main body 1 and can hold the lower end plate 17. In the above, it is also possible to apply various release materials to the inner surface of the steel pipe 20 and then pour concrete material into the steel pipe 20.

[0021] 3. Construction of foundation piles 60

[0022] (1) For example, a case where a connected precast pile 51 (FIG. 3) is formed from a lowermost precast pile 52B, a lower precast pile 52A and a precast pile 50 will be described.

[0023] (2) Excavate pile holes 56 from above ground 55 using any excavation means, and form pile holes 56 by filling them with cement milk (hydraulic material) (FIG. 4(a)).

[0024] (3) Using conventional means, the lowest precast pile 52B is lowered into the pile hole 56, and the lower precast pile 52A is connected to the upper end of the lowest precast pile 52B and lowered (FIG. 4(b)).

[0025] (4) The lower precast pile 52A to which the lowest precast pile 52B is connected is held on the ground 55, and the precast pile 50 is lowered from above (FIG. 4(c)), and the lower end plate 17 of the precast pile 50 is connected to the upper end plate 53 of the lower precast pile 52A in a normal manner (FIG. 4(d)). The lowest precast pile 52B, the lower precast pile 52A, and the precast pile 50 are connected to form the connected precast pile 51. In this case, the lower end plate 17 of the precast pile 50 and the upper end plate 53 of the lower precast pile 52A are both engaged with an outer diameter D2 and an inner diameter D0, so that they can be connected by ordinary means (various mechanical joints or welding) without using any special method.

[0026] (5) Next, the connected precast piles 51 (the lowermost precast pile 52B, the lowermost precast pile 52A, and the precast pile 50) are lowered to a predetermined depth. Usually, the lower end of the lowermost precast pile 52B is buried in the pile hole 56 at a position slightly above the bottom of the pile hole 56. Note that the position of the lower end of the lowermost precast pile 52B in the pile hole 56 is optional, and the lower end of the lowermost precast pile 52B can be grounded on the bottom of the pile hole 56 (not shown).

[0027] (6) Once the cement milk has solidified, the foundation pile 60 of the present invention is formed (FIG. 4(e)).

[0028] (7) Other embodiments In the above embodiment, the configuration of the connected precast pile 51 includes a precast pile 50 and a lower precast pile 52A directly below it, and the number and structure of the precast piles connected below the lower precast pile 52A are optional (not shown). In addition, in the above embodiment, the connected precast piles 51 (precast pile 50, lower precast pile 52A) are buried in the pile hole filled with cement milk, but it is also possible to excavate the pile hole 55 while burying the precast pile 50, lower precast pile 52A, etc. (not shown). In the above embodiment, cement milk is used as the hydraulic material, but any commonly used cement-based material such as soil cement may be used.

[0029] 4. Other embodiments of prefabricated piles

[0030] (1) In the above embodiment, the lower end 22 of the steel pipe 20 is located near the upper end of the reduced diameter portion 10 depending on the ground conditions, etc., but it may be located sufficiently above the upper end of the reduced diameter portion 10 (not shown). In other words, the lower end 22 of the steel pipe 20 is located near the center or upper end of the precast pile main body 1 in the axial direction.

[0031] (2) In addition, in the above embodiment, a reduced diameter portion 10 is formed in the prefabricated pile body 1, but it is also possible to form a straight prefabricated pile body that does not form the reduced diameter portion 10, or to form a large diameter portion instead of the reduced diameter portion (not shown). [Explanation of symbols]

[0032] 1 Prefabricated pile body 6. Hollow part of prefabricated pile body 10. Reduced diameter part of prefabricated pile body 11 Steep slope of narrowed section 12 Gentle slope of narrowed section 15 Top end plate 17 Lower end plate 20 Steel pipe 21 Upper end of steel pipe 22 Lower end of steel pipe 22a Bottom end of steel pipe 31 Lower formwork jig 50 Prefabricated piles 51 Connected prefabricated piles 52A Lower Prefabricated Pile 52B Bottom prefabricated pile 53 Upper end plate of lower prefabricated pile 55 Ground 56 Pile hole 57 Cement milk (hydraulic material) 60 Foundation pile (foundation pile structure)

Claims

1. A precast concrete pile covered with a steel pipe, characterized in that the precast concrete pile body is configured by disposing a steel pipe around the outer periphery of the precast concrete pile body as described below. (1) An upper pile end plate is provided at the upper end of the precast pile body, and a lower pile end plate is provided at the lower end of the precast pile body. (2) The upper end of the steel pipe was fixed to the upper pile end plate at the upper end of the precast pile body. (3) The lower end of the steel pipe was not fixed to the lower end plate of the precast pile body, and the lower end of the steel pipe was positioned above the lower end plate of the precast pile body.

2. 2. A precast concrete pile covered with a steel pipe as described in claim 1, characterized in that the inner diameter of the precast pile body is kept the same, the lower end of the outer surface of the precast pile body is reduced in diameter to form a reduced diameter portion, and the outer diameter of the lower end plate is made smaller than that of the upper end plate.

3. 3. A precast concrete pile covered with a steel pipe according to claim 2, characterized in that it is constructed as follows: (1) The lower end of the precast pile body was gradually reduced in diameter to form a reduced diameter section, and the outer diameter of the lower end plate was made smaller than that of the upper end plate. (2) The lower end of the steel pipe was positioned at the same position as the upper end of the reduced diameter portion or higher than the upper end of the reduced diameter portion.

4. A connected precast pile is formed by connecting the lower end plate of a concrete upper precast pile with a diameter of D2 covered with a steel pipe to the upper end plate of a concrete lower precast pile with a diameter of D1, which may or may not be covered with a steel pipe. A foundation pile structure characterized by being buried in a pile hole and configured as follows. (1) The upper precast pile was constructed as follows: (a) An upper pile end plate having an outer diameter D1 is provided at the upper end of the precast pile body, a lower pile end plate having a diameter D2 is provided at the lower end of the precast pile body, and a reduced diameter portion is formed at the lower end of the precast pile body, such that D2 < D1. (b) The upper end of the steel pipe was fixed to the upper pile end plate of the precast pile body. (c) The lower end of the steel pipe was not fixed to the lower end plate of the precast pile body, and the lower end of the steel pipe was positioned above the lower end plate of the precast pile body. (2) A hydraulic material was filled between the pile hole and the outer periphery of the connected precast pile. (3) The upper precast pile was "located near the ground" or "located at the top of the precast pile."

5. 5. The foundation pile structure according to claim 4, characterized in that it is configured as follows. (1) The lower end of the connecting precast pile body of the upper precast pile was gradually reduced in diameter to form a reduced diameter portion. (2) The lower end of the steel pipe was positioned at the same level as or higher than the upper end of the reduced diameter portion.

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