JP2004211478A - Foundation pile body and its construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foundation pile body having sufficient bending yield strength as the foundation work of a bridge pier or the like and constructible at a low cost, and its construction method. <P>SOLUTION: This foundation pile body is provided with a long cylindrical prestressed concrete well part 11 formed by connecting a plurality of short cylindrical bodies 13 sunk in a ground upper layer part 2, in the center axial direction and integrating them, and a cast-in-place pile part 12 integrated with the prestressed concrete well part 11 by placing concrete as far as the inner space of the prestressed concrete well part 11, and arranged in the lower layer part of the ground 2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pile body for a foundation mainly used as a foundation work such as a pier and a method for constructing the pile body.
[0002]
[Prior art]
Conventionally, in the case of foundation works such as piers, if the supporting layer made of sand and gravel is located at a deep position and the intermediate layer from the ground surface to the supporting layer requires high bending strength, PC well A structure using a construction method is used as a foundation work (for example, see Patent Document 1).
[0003]
In this PC well method, a plurality of short cylinders 1, 1... Made of precast concrete are sunk while being press-fitted, and as shown in FIG. 3 is constructed, a PC steel material is arranged over the entire length of the PC well structure 3 in the central axis direction, and a prestress is applied to the entire structure by tensioning the PC steel material so that a large bending strength can be obtained. I have.
[0004]
FIG. 8A is a cross-sectional view showing the state of the stratum of the ground on which the base PC well structure 3 is laid, and FIG. 8B is a graph showing the ground strength (N value). A support layer composed of gravel and the like with high ground strength (N value) is formed at a deep position in the ground, and layers of clay, sand, silt, and the like with relatively low ground strength are laminated from the support layer to the surface of the ground. I have.
[0005]
[Patent Document 1]
JP-A-11-152746 (0018 paragraph, 0026 paragraph, etc.)
[0006]
[Problems to be solved by the invention]
However, in the conventional technique as described above, the joining between the short cylinders has a structure in which the joining surfaces are directly abutted with each other, and the production accuracy of the joining end face of the short cylinder needs to be extremely high. There is a problem in that the cost of manufacturing the cylindrical body is high, and if the entire length of the foundation structure is constructed by the PC well method when the support layer is at a deep position, it becomes very expensive.
[0007]
The present invention has been made in view of the state of the related art, and has as its object to provide a foundation pile having sufficient bending strength as a foundation for a pier or the like and which can be constructed at low cost, and a method of constructing the same.
[0008]
[Means for Solving the Problems]
In order to solve the conventional problems as described above and to achieve the intended purpose, the invention of claim 1 is a long-sized structure in which a plurality of short cylinders disposed in the upper layer of the ground are connected in a central axis direction and integrated. It is provided with a cylindrical PC well portion and a cast-in-place pile portion integrated with the PC well portion by pouring concrete up to an inner space of the PC well portion and arranged in a lower part of the ground. It is characterized by.
[0009]
With such a configuration, it is possible to reduce the number of expensive short cylinders and to construct them at low cost while securing sufficient bending strength.
[0010]
According to a second aspect of the present invention, in addition to the configuration of the first aspect, the short cylindrical body has a tubular steel pipe and a concrete tubular body cast on an inner peripheral portion of the steel pipe.
[0011]
With this configuration, if the pile diameter is the same, the bending strength of the PC well can be made larger than that of the steel pipe soil cement pile method, the steel pipe pile, the cast-in-place pile, and the like.
[0012]
According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, the short cylinder is formed by connecting arc-shaped blocks each having a shape obtained by dividing an annular ring into two or more in a circumferential direction. I do.
[0013]
With this configuration, it is possible to suitably cope with a pile having a large diameter.
[0014]
According to the invention of claim 4, a long cylindrical PC well portion in which a plurality of short cylinders are connected in the central axis direction and integrated is settled in the upper layer of the ground, and then connected to the inner space of the PC well portion. Excavating the ground downward, placing concrete in the excavated cast-in-place hole, placing the concrete down to the inner space of the PC well portion, and ending the PC It is characterized in that a cast-in-place pile portion fitted to the inner portion of the well portion is formed.
[0015]
With such a configuration, it is possible to provide a sufficient strength as a foundation work and to construct it at low cost.
[0016]
According to a fifth aspect of the present invention, in addition to the configuration of the fourth aspect, a short cylinder is formed by connecting arcuate blocks each having a shape obtained by dividing an annular ring into two or more in the circumferential direction.
[0017]
With this configuration, even a pile having a large diameter can be suitably adapted.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of a foundation pile according to the present invention will be described with reference to the drawings. The same parts as those in the above-described embodiment will be described with the same reference numerals.
[0019]
FIG. 1C shows a state in which the foundation pile according to the present invention has been submerged in the ground, where reference numeral 10 denotes a foundation pile, and reference numeral 2 denotes a ground.
[0020]
FIG. 1A is a cross-sectional view illustrating a state of the stratum of the ground where the foundation pile 10 is laid, and FIG. 1B is a ground strength (N) of the ground where the foundation pile 10 is laid. 8, the ground 2 has a support layer made of gravel or the like having a high ground strength suitable for supporting a foundation pile, as in the conventional example shown in FIG. And a layer having relatively low ground strength (N value), such as clay, sand, silt, etc., is stacked from the support layer to the ground surface.
[0021]
The foundation pile 10 includes a PC well 11 and a cast-in-place pile 12 projecting from a lower edge of the PC well 11, and the PC well 11 and the cast-in-place pile 12 are integrally formed. I have.
[0022]
The PC well portion 11 is formed in a long cylindrical shape in which a plurality of short cylinders 13, 13,... Are connected in a central axis direction to be integrated, and a PC steel material 14 is provided on the peripheral wall over the entire length in the central axis direction. The prestress is applied to the entire PC well portion 11 by being inserted and tensioning the PC steel material 14.
[0023]
As shown in FIG. 2, the PC steel material 14 is tensioned at the upper end of each short cylinder 13 and is fixed on the upper supporting plate 16 using the coupler 15, and the upper PC steel material 14 is connected thereto. The short cylinders that are sequentially applied with a prestress and are vertically connected to each other are connected to each other.
[0024]
The total length of the PC well portion 11, that is, the number of short cylinders connected in the central axis direction is a length having a sufficient bending strength according to the horizontal stress acting on the pile, the bending moment, the strength of each layer portion, and the like. Is determined.
[0025]
As shown in FIG. 3, the short cylindrical body 13 has a cylindrical steel pipe 17 and a concrete cylindrical body 18 which is formed into a cylindrical shape on an inner peripheral portion of the steel pipe 17. The shape 18 is integrated. Reference numeral 19 in the drawing denotes an insertion hole through which the PC steel material 14 passes.
[0026]
The cast-in-place pile portion 12 is formed in a rod shape of a reinforced concrete structure having a reinforcing bar cage 20 therein, and cast-in-place concrete is cast into the inner space 11 a of the PC well portion 11 and integrated with the PC well portion 11. ing.
[0027]
The outer diameter of the cast-in-place pile 12 is formed smaller than the outer diameter of the PC well 11.
[0028]
The reinforcing rod cage 20 is provided with a number of vertical bars 21, 21... In a parallel arrangement spaced apart in the circumferential direction, and laterally restraining bars 22, 22,. The vertical streaks 21 and the horizontal restraining streaks 22 are arranged in a spiral shape, and are combined in a cage shape.
[0029]
Note that the number of the vertical streaks 21 is determined in consideration of the strength of the ground layer at the portion where the vertical streaks are installed, the strength of the ground layers at various places, the horizontal strength to act, the bending moment, and the like. Further, a two-stage arrangement in which the number of vertical stripes is different in the upper and lower portions may be adopted.
[0030]
This foundation pile 10 uses a PC well 11 having a large bending strength in the upper layer of the ground requiring a large horizontal strength, and a cast-in-place pile 12 made of cast-in-place concrete, which is inexpensive to implement, in the lower layer of the ground. For example, as in the example shown in FIG. 5, the resistance bending moment exceeds the bending moment in both the PC well portion and the cast-in-place pile portion with respect to the bending moment in the ground. In addition to the above, the ratio of the expensive PC well structure portion can be reduced as compared with the foundation pile having the entire length of the pile formed by the PC well structure.
[0031]
Next, a method of constructing the above-described foundation pile will be described with reference to FIGS.
[0032]
First, as shown in FIG. 6A, at a construction site of a foundation pile, a guide frame 23 for constructing a PC well portion is installed and fixed on the ground surface.
[0033]
Next, as shown in FIG. 6 (b), a steel blade 24 is attached to the lower end of the short cylinder 13 to form a blade block 25 composed of the short cylinder 13 and the steel blade 24. The mouth block 25 is placed in the guide frame 23, the level of the blade block 25 is measured, and if necessary, pressure is applied to the blade block 25 by a not-shown submersible jack to secure the horizontality of the blade block 25.
[0034]
Then, the sinking jack is connected to the short cylindrical body 13, and the inside of the short cylindrical body 13 is excavated in conjunction with the pressurization by the sinking jack, so that the blade block 25 is sunk.
[0035]
Next, the short cylinder 13 is superimposed on the blade block 25 (short cylinder 13) by applying a resin-based adhesive such as an epoxy resin adhesive to the joint end face, and further excavating the inside of the short cylinder. Lower the whole.
[0036]
This operation is repeated until the uppermost short cylindrical body 13 is connected (FIG. 6C).
[0037]
On the other hand, during this work, the PC steel 14 is tensioned at the upper end of each short cylindrical body 13 and is fixed on the upper support plate 16 using the coupler 15, and the upper PC steel 14 is connected thereto. The short cylinders that are sequentially applied with a prestress and are vertically connected to each other are connected to each other.
[0038]
Then, the PC steel material 14 into which the peripheral wall portions of the short cylindrical bodies 13 are inserted is tensioned at the upper end of the PC well portion 11 as shown in FIG. 11 is pre-stressed in the central axis direction.
[0039]
The insertion hole 19 of each short cylinder into which the PC steel material 14 is inserted is filled with grout or the like.
[0040]
Then, as shown in FIG. 6E, the inside of the short cylindrical body 13 is excavated, and at the same time, the entire PC well 11 is lowered to a desired depth by press-fitting with the immersion device 26.
[0041]
This submerging device 26 has a pressing plate 26b having jacks 26a and 26a at the upper end of the PC well portion 11 and pulls the press-fitting lot 26c supported by the guide frame 23 by the jack 26a. 26b is pulled down by applying a reaction force to the guide frame 23, and the PC well 11 is pressed by the pressing plate 26b to be pressed into the ground.
[0042]
Thus, the step of constructing the PC well section 11 is completed.
[0043]
Next, the inner bottom of the PC well 11 submerged in the ground is excavated downward so as to form a cast-in-hole 27 continuous with the inner space 11a of the PC well.
[0044]
The excavation of the cast-in-place hole 27 is performed by a reverse method, and as shown in FIG. 7A, the ground 2 is excavated by rotating the excavation head 29 provided at the tip of the reverse pipe 28, and the reverse pipe 28 is excavated. The excavated earth and sand is discharged through the ground.
[0045]
Then, the ground is excavated until the ground reaches a predetermined depth, that is, a depth reaching the support layer, so that the cast-in-place hole 27 is formed.
[0046]
Next, as shown in FIG. 7 (b), when the reinforcing rod cage 20 is hung down into the casting hole 27 through the inner space 11a of the PC well portion, as shown in FIG. The cast-in-place pile 12 is formed by placing and casting underwater concrete into the cast-in-place hole 27 by cast-in-place (FIG. 7D).
[0047]
At this time, as shown in FIG. 7 (e), the underwater concrete is poured (filled) to a position where it reaches the PC well portion 11, and then is subjected to necessary hardening and curing. Are fitted inside the PC well 11, and the PC well 11 and the cast-in-place pile 12 are integrated.
[0048]
In this way, the PC well portion 11 is arranged in the upper layer of the ground where relatively large bending strength is required, and the cast-in-place pile 12 formed of inexpensive cast-in-place concrete is arranged in the lower layer of the ground. The pile body 10 is constructed.
[0049]
Note that the short cylindrical body 13 may have a structure in which arc-shaped blocks each having a shape obtained by dividing an annular ring into two or more are connected in the circumferential direction to be cylindrical.
[0050]
Further, in the above-described embodiment, the example in which the excavation of the cast-in-place hole 27 is performed by the reverse method is described, but the excavation may be performed by another method.
[0051]
【The invention's effect】
As described above, the pile body for foundation according to the present invention uses a PC well portion having a large bending strength in the upper layer of the ground where relatively large bending strength is required, and is constructed at a low cost in the lower layer of the ground. By using cast-in-place piles that can be used, it satisfies sufficient bending strength as a foundation work, and simplifies construction by making the expensive PC well structure only the part corresponding to the upper layer of the ground In addition, the cost of the entire pile body can be reduced, and the pile body can be constructed at low cost.
[0052]
By having a tubular steel pipe and a concrete tubular body cast in the inner peripheral part of the steel pipe, if the pile diameter is the same, the bending strength of the PC well part is obtained by a steel pipe soil cement pile method, It can be larger than steel pipe piles and cast-in-place piles.
[Brief description of the drawings]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a cross-sectional view for explaining the ground layer on which a foundation pile according to the present invention is laid, FIG. 1B is a graph showing the ground strength, and FIG. It is a longitudinal cross-sectional view which shows an example of implementation of.
FIG. 2 is a partially enlarged sectional view showing a connected state of a PC well portion in FIG.
FIG. 3 is a cross-sectional view showing the short cylinder of the above.
FIG. 4 is a partially enlarged sectional view showing a cast-in-place pile portion in FIG. 1;
FIG. 5 is a graph showing an example of a bending moment diagram of the same foundation pile.
FIGS. 6 (a) to 6 (e) are explanatory views showing steps of constructing a PC well portion in FIG.
7 (a) to 7 (e) are explanatory diagrams showing a construction step of a cast-in-place pile portion in FIG. 1;
8 (a) is a cross-sectional view illustrating the state of the ground on which the conventional foundation structure is laid, FIG. 8 (b) is a graph showing the same ground strength, and FIG. It is a longitudinal section showing an example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Foundation pile 11 PC well 12 Cast-in-place pile 13 Short cylindrical body 14 PC steel 15 Coupler 16 Upper support plate 17 Steel pipe 18 Concrete cylindrical body 19 Insertion hole 20 Reinforcing cage 21 Vertical streak 22 Horizontal restraint 23 Guide frame Reference Signs List 24 steel cutting port 25 cutting port block 26 setting device 27 casting hole 28 reverse pipe 29 drilling head 30 tremy pipe

Claims (5)

A long tubular PC well section in which a plurality of short cylinders laid down in the upper layer of the ground are connected in the central axis direction and integrated, and by casting concrete to reach the inner space of the PC well section, A pile body for foundation, comprising: a cast-in-place pile section integrated with the PC well section and arranged in a lower part of the ground. 2. The foundation pile according to claim 1, wherein the short cylindrical body includes a tubular steel pipe and a concrete tubular body cast on an inner peripheral portion of the steel pipe. 3. 3. The foundation pile according to claim 1, wherein the short cylindrical body is formed by connecting arcuate blocks each having a shape obtained by dividing an annular ring into two or more in a circumferential direction. 4. After the long cylindrical PC well portion in which a plurality of short cylinders are connected in the central axis direction and integrated is settled in the upper layer portion of the ground, the ground is lowered so as to be continuous with the inner space of the PC well portion. The concrete is cast into the excavated cast-in-place hole by cast-in-place, and the concrete is cast into the inside space of the PC well portion, and cast in place with the PC well portion. A method for constructing a pile for foundation, characterized by forming a pile. The method for constructing a pile for foundation according to claim 4, wherein the short cylindrical body is formed by connecting arc-shaped blocks each having a shape obtained by dividing an annular ring into two or more in a circumferential direction.

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