JPH08296225A - Precast concrete pile and method for integrally constructing precast concrete pile and foundation - Google Patents

Abstract

PURPOSE: To restrict the lowering of the proof stress of a precast concrete pile due to the reduction of the led prestress in the case where the PC pile is cut off. CONSTITUTION: A precast concrete pile 10, in which a tensile fixation part 14 of a precast concrete steel material 12 embedded in the tensile condition is arranged inside a pile head and the unbonding is performed to the PC steel material 12 between the tensile fixation part 14 and the upper end 10b of the pile head, is used, and after placing the PC pile 10 under the ground, the PC pile 10 is cut off between the tensile fixation part 14 and the upper end 10b of the pile. The foundation concrete 16 is placed around the pile head of the PC pile 10 for integration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated construction method of a PC pile and a foundation and a PC pile. More specifically, when the PC pile is cut off, the strength of the PC pile is reduced by reducing the prestress introduced. The present invention relates to an integrated construction method of a PC pile and a foundation capable of suppressing the deterioration of the PC pile and a PC pile used for this method.

[0002]

2. Description of the Related Art Conventionally, a cylindrical PC (Prestressed concrete) in which a prestress is introduced by a PC steel material is used as a pile for supporting loads of various structures through the foundation such as footings and foundation slabs in the ground. Piles are widely used. According to this PC pile, since a large bending rigidity is obtained by the introduced prestress, there is an advantage that the safety against driving is high and an excellent yield strength is obtained even after driving. FIG. 4 shows such a conventional PC pile. This PC pile 1 has a plurality of PC steel materials 3 axially inserted into a concrete 2 having a cylindrical shape, and is prestressed. The fixing end portions 4 provided at both ends are fixed.

In order to integrate the PC pile 1 and the footing (foundation) having the above structure, as shown in FIG. 5, first, a predetermined number of the PC piles 1 are driven into the ground, and then the mutual PCs are put together. In order to adjust the pile head level of the pile 1, the pile head 1a is cut off at a position protruding from the ground by a predetermined dimension. At this time, the upper end portion 3a of the PC steel material 3 of each PC pile 1
Is cut at a position where it extends a predetermined length from the cut-off upper end surface 1b in order to form a reinforcing bar at the joint with the footing 5, and then the pile head of the PC pile 1 is surrounded by concrete. Footing 5 by placing
And the footing 5 and the PC pile 1 are integrated.

[0004]

However, in the conventional method of integrating a PC pile and a foundation using the above-mentioned PC pile 1, as is well known, the pile head 1a of the PC pile 1 is cut off. In doing so, 30 to 50% of the prestress introduced by the PC steel material 3 is lost, resulting in the above P
Since the proof stress of the C pile 1 is lowered and the pile head 1a may be damaged particularly when a horizontal force is applied, it is necessary to use the PC pile 1 having a higher pile diameter or strength rank in advance. There was a drawback. Therefore, a conventional PC that compensates for the decrease in prestress at the time of cutting off the pile head 1a
As a method for integrating piles and foundations, Japanese Patent Publication No. 2-43848
What is found in the publication is known.

FIG. 6 and FIG. 7 show P in the above publication.
This shows an integrated construction method of the C pile 1 and the footing 5. In this integrated construction method, first, as shown in FIG. 6, a PC pile in which a plurality of PC steel materials 3 are embedded in concrete 2 in a tensioned state. After driving 1 into the ground to a predetermined depth,
Cut off the pile head 1a of the PC pile 1 protruding above the ground. At this time, the PC steel material 3 is not cut off and left as it is as the protruding portion 3b, and as shown in FIG. 7, concrete is cast to form the footing 5, and then the protruding portion 3b is tensioned. Then, the prestress is introduced. According to such an integrated method, after the footing 5 is formed, the pile head 1a and the footing 5 are
It is said that, by introducing prestress between the PC pile 1 and the footing 5, the prestress reduced when the PC pile 1 is cut off can be recovered.

However, in the above-mentioned conventional method of integrating the PC pile and the foundation, the pile head 1 of the PC pile 1 is constructed.
When the a is cut off, the PC steel material 3 that is in close contact with the concrete 2 is deformed, and it is actually extremely difficult to bend it into a straight line as shown in FIG. There was a point. In addition, since the protruding portion 3b of the PC steel material 3 and the footing 5 are in close contact with each other, it is difficult to introduce sufficient prestress to the PC pile 1 even if the PC steel material 3 is re-tensioned. The present invention
The present invention was made to effectively solve the problems of the above-mentioned conventional PC pile and a method of integrating a PC pile and a foundation using the same, and reduces the prestress introduced when the PC pile is cut off. It is an object of the present invention to provide an integrated construction method of a PC pile and a foundation capable of suppressing a decrease in yield strength of the PC pile due to the above, and a PC pile used for this method.

[0007]

According to a first aspect of the present invention, there is provided a PC pile according to the present invention, in which a tension fixing portion of a PC steel material is disposed inside a pile head, and the tension fixing portion is provided between the tension fixing portion and an upper end of the pile head. It is characterized in that the unbonded PC steel material is applied. Here, as the unbonding treatment, as in the invention described in claim 2, a configuration in which a sheath is provided on the outer circumference of the PC steel material, or in the invention described in claim 3, the P bonding is performed.
It is possible to apply a configuration in which a coating film that prevents adhesion to concrete is formed on the outer periphery of the C steel material.

The invention according to claim 4 is an integrated construction method of a PC pile and a foundation using the PC pile according to any one of claims 1 to 3, wherein the PC pile is underground. After striking into
The C pile is cut off, and then basic concrete is placed around the pile head of the PC pile to integrate it. Further, in the invention according to claim 5, after driving the PC pile in which the PC steel material is tensioned into the ground, a part of the PC steel material is projected from the upper end of the pile head after cutoff. The pile head of the PC pile is cut off, and then an unbonded PC steel material is connected to the upper end of the PC steel material to cast a foundation concrete, and then the unbonded P
It is characterized in that prestress is introduced into the PC pile through the C steel material.

[0009]

In the PC pile according to claims 1 to 3,
In both cases, if the PC pile is cut off between the tension anchoring portion of the PC steel and the upper end of the pile head, the prestress is released only above the tension anchoring portion, but the prestress in the lower portion from the tension anchoring portion is released. There is no reduction in stress. Therefore, the PC according to claim 4 using the PC pile according to any one of claims 1 to 3 above.
According to the integrated method of the pile and the foundation, when the PC pile is driven into the ground and then the PC pile is cut off between the tension fixing portion of the PC steel material and the upper end of the pile head, the PC pile is ,
Since the prestress in the portion below the tension fixing portion is not reduced at all and the initial state is maintained as it is, the cutoff does not reduce the yield strength of the PC pile.

On the other hand, according to the invention of claim 5, since the unbonded PC steel material is connected to the upper end portion of the PC steel material projected from the upper end of the pile head of the PC pile at the time of cut-off, the foundation concrete is poured. After that, since the unbonded PC steel material and the concrete do not adhere to each other, the unbonded P
It becomes possible to reintroduce the prestress reduced at the time of cut-off to the PC pile with a small tension through the C steel material. At this time, since only a part of the PC steel material is projected from the upper end surface of the cut-off PC pile and the unbonded PC steel material is connected thereto, the construction is easy. By the way, as a part of the PC steel material that is projected from the top end surface of the cut-off PC pile, the PC steel material and the unbonded P
It is sufficient if the length dimension is sufficient to connect the C steel material.

[0011]

[Embodiment 1] FIG. 1 shows an embodiment of a PC pile of the present invention, in which a plurality of Ps are provided in a concrete 11 having a cylindrical shape.
The C steel material 12 is inserted in the axial direction, and after the prestress is introduced, the structure fixed at the fixing end portions 13 provided at both ends is the same as that shown in FIG. In 10, the pile head 10a
The tension fixing portion 14 of the PC steel material 12 is embedded in a position of a predetermined size from the pile head upper end 10b, and the PC steel material 12 between the tension fixing portion 14 and the pile head upper end 10b is unbonded. It has been subjected. Here, the position where the tension fixing portion 14 is embedded may be set to a position slightly lower than the position where the PC pile 10 may be cut off when driven into the ground. preferable. In addition, the unbonding treatment is performed in the above-mentioned P
This is done by covering the outer circumference of the C steel material 12 with a sheath 15. In addition, as this unbonding treatment, oil or asphalt may be applied to the outer circumference of the PC steel material 12 or a tape may be wound to form a film for preventing the adhesion with the concrete 11. .

Next, with reference to FIGS. 1 and 2, a first embodiment of a method for integrating a PC pile and a foundation according to the present invention, which uses the PC pile 10 having the above structure, will be described.
First, after driving the plurality of PC piles 10 shown in FIG. 1 into the ground, in order to adjust the pile head level of the PC piles 10 to each other, the PC piles 10 are fixed to the tension fixing portion 14 and the pile head upper end. 10
Cut off at the desired position between b and b. At this time, the upper end portion 12a of the PC steel material 12 of each PC pile 10 has a predetermined length from the pile head upper end 10c after being cut off in order to make a bar arrangement at a joint with a footing (foundation) 16 described later. Cut at the extended position. Then, by placing concrete so as to surround the pile heads of the PC pile 10, a footing 16 is constructed as shown by a chain line in FIG.
The C pile 10 is integrated.

As described above, the PC using the PC pile 10
According to the integrated method of the pile and the foundation, after the PC pile 10 is driven into the ground, the PC pile 10 is cut off between the tension fixing portion 14 of the PC steel material 12 and the pile head upper end 10b. As a result, the prestress is released only from the tension fixing portion 14 above the prestress-free portion, and the prestress initially applied in the lower portion from the tension fixing portion 14 requiring prestressing as the PC pile 10 is There is no reduction. Therefore, the PC pile 10
Since the initial prestressing state of the PC pile can be maintained as it is, the proof stress of the PC pile 10 does not decrease due to the above-mentioned cut-off, and therefore, the pile diameter or strength level based on the prestressing force applied at the time of manufacturing should be used. It can be used as it is.

[0014]

[Embodiment 2] FIG. 3 shows a second embodiment of the method for integrating a PC pile and a foundation according to the present invention. In this embodiment, first, a plurality of PCs in which a PC steel material 21 is tensioned are provided. Pile 20
After driving into the ground, the pile heads 20a of the PC piles 20 are cut off at desired positions in order to adjust the mutual pile head levels of the PC piles 20. At this time, the cut-off is performed so that a small portion 21a of the PC steel material 21 projects from the pile head upper end 20b after the cut-off. Next, the unbonded PC steel material 23 is connected to the upper end portion of the PC steel material 21 via the grip joint 24. Therefore, as the length dimension of the part 21a of the PC steel material 21 which is projected from the pile head upper end 20b, the unbonded PC steel material 2 is previously prepared.
The grip joint 24 attached to the lower end of
It is sufficient that the length dimension is sufficient to connect the. Also,
As the unbonded PC steel material 23, as in the case of the first embodiment, it is possible to use a material in which a sheath 27 is put on the outer circumference of the PC steel material. Next, the pile head 20a of the PC pile 20
Placing foundation concrete around and footing (foundation)
25, and the fixing portion 26 is formed on the upper surface of the footing 25 where the unbonded PC steel material 23 projects. Then, after the footing 25 is constructed, the unbonded PC steel material 23 is tensioned to
Introduce prestress to the pile 20.

According to the integrated method of the PC pile and the foundation of this example, a part 21a of the PC steel material 21 is slightly projected from the pile head upper end 20b of the PC pile 20 at the time of cut-off, and the unbonded PC is attached to this upper end. Since the steel material 23 is connected, the unbonded PC steel material 2 is formed after the footing 25 is placed.
Since 3 and the concrete forming the footing 25 do not adhere to each other, only a small tension force is applied through the unbonded PC steel material 23, and the prestress reduced at the time of cutoff is effectively reintroduced into the PC pile 20. Is possible. At this time, since only a part 21a of the PC steel material 21 is projected from the pile head upper end 20b of the cut-off PC pile 20 and the unbonded PC steel material 23 is connected thereto, the bending of the PC steel material 21 is performed. The construction can be easily performed without the need for correction or the like.

In the explanation of the second embodiment,
Although only the example in which the PC steel material 21 and the unbonded PC steel material 23 are connected by the grip joint 24 has been described, the invention is not limited to this, and various connection tools such as a coupler or direct welding may be used.

[0017]

As described above, according to claims 1 to 3,
According to the PC pile described in (1), by cutting off the PC pile between the tension fixing portion and the upper end of the pile head of the PC steel material, the prestress in the lower portion from the tension fixing portion is reduced. According to the integrated method of the PC pile and the foundation according to claim 4 in which the PC pile is used, the above-mentioned PC pile is driven into the ground after the PC pile is driven. By cutting off between the tension anchoring portion of the PC steel material and the upper end of the pile head, the prestress initially applied is not reduced in any portion from the tension anchoring portion to the lower portion. Since it is possible to maintain the prestressed state of the PC pile as it is, the yield strength of the PC pile does not decrease, so it is possible to use the pile diameter or strength level according to the initial prestressing force. That.

Further, according to the invention of claim 5, a part of the PC steel material is slightly projected from the upper end of the pile head of the PC pile at the time of cutoff, and the unbonded PC steel material is connected to the upper end portion. After the footing is cast, the unbonded PC steel material and the concrete forming the footing do not adhere to each other, and as a result, only a small tension force is applied through the unbonded PC steel material, and the PC is effectively
It is possible to re-introduce the prestress reduced at the cut-off to the pile, and only part of the above PC steel material is projected from the top end of the pile head of the cut-off PC pile, and the unbonded PC steel material is connected to this. Therefore, it is not necessary to correct the bending of the PC steel material, and the construction can be easily performed.

[Brief description of drawings]

FIG. 1 is a side sectional view of an essential part showing an embodiment of a PC pile of the present invention.

FIG. 2 is a side sectional view showing a first embodiment of a method for integrating a PC pile and a foundation according to the present invention using the PC pile shown in FIG.

FIG. 3 is a side sectional view showing a second embodiment of the method for integrating a PC pile and a foundation of the present invention.

FIG. 4 is a side sectional view of a main part showing a conventional PC pile.

FIG. 5 is a side sectional view showing a conventional method of integrating a PC pile and a foundation using the PC pile of FIG.

FIG. 6 is a side sectional view showing a state at the time of cutting off a PC pile in another conventional method of integrating a PC pile and a foundation.

FIG. 7 is a side sectional view showing a state in which the PC pile and the foundation of FIG. 6 are integrated.

[Explanation of symbols]

 10, 20 PC pile 10a, 20a Pile head 10b, 10c, 20b Pile head upper end 11 Concrete 12, 21 PC steel material 12a PC steel material upper end portion 14 Tension fixing part 15, 27 Sheath 16, 25 Footing (foundation) 21a PC steel material Part 23 Unbonded PC steel 24 Grip joint 26 Fixing part

Front page continuation (72) Inventor Mark Renchener 1-25-1 Nishishinjuku, Shinjuku-ku, Tokyo Taisei Construction Co., Ltd. (72) Inventor Shiho Saito 1-25-1 Nishishinjuku, Shinjuku-ku, Tokyo Taisei Construction Co., Ltd. In the company

Claims (5)

[Claims] 1. In a PC pile in which a PC steel material is tensioned, a tension fixing portion of the PC steel material is provided in a pile head,
A PC pile, wherein the PC steel material between the tension fixing portion and the upper end of the pile head is unbonded. 2. The unbonding treatment is performed by coating a sheath on the outer periphery of the PC steel material.
PC pile described in. 3. The PC pile according to claim 1, wherein the unbonding treatment is performed by forming a coating film on the outer periphery of the PC steel material to prevent adhesion to concrete. 4. P according to any one of claims 1 to 3.
After driving the C pile into the ground, the PC pile is cut off between the tension anchoring portion and the upper end of the pile head, and then foundation concrete is placed around the pile head of the PC pile to integrate it. An integrated construction method for PC piles and foundations, which is characterized in that 5. After driving a PC pile in which PC steel material is tensioned into the ground, the above P from the top end of the pile head after cutoff
After cutting off the pile head of the PC pile so that a part of the C steel material protrudes, and then connecting the unbonded PC steel material to the upper end portion of the PC steel material and placing the basic concrete, the unbonded PC steel material An integrated construction method of a PC pile and a foundation, characterized in that prestress is introduced into the PC pile via the above.