JPH0751778B2 - Expanding method of expanding circular pile and circular arc pile - Google Patents

Description

TECHNICAL FIELD The present invention relates to an expanded circular arc pile and a method for expanding the circular arc pile, and particularly to reduction of the number of piles.

[Prior Art] Pile foundations are used to ensure sufficient ground strength against loads such as buildings and civil engineering structures. The piles can be roughly divided into ready-made piles and cast-in-place piles.

Ready-made piles are made on site or in factories and consist of concrete piles or steel piles. As for the cast-in-place pile, there are an excavation method of placing concrete after excavation and a penetration method of placing concrete after penetration. This cast-in-place pile has less noise and vibration than the hammering method for ready-made piles, and since it does not drive in, it has little effect on neighboring structures due to vibration and is widely used for construction in urban areas. As described above, the piles are classified according to the manufacturing method and the installation method, and conventionally, all the piles are linear piles.

Usually, the bearing capacity of a pile is considered to be the sum of the bearing capacity at the tip of the pile and the bearing capacity due to the friction on the peripheral surface of the pile. The pile tip supporting force is proportional to the area of the pile tip, and the supporting force due to friction on the peripheral surface is proportional to the pile perimeter. That is, when a straight pile is used as in the conventional case, the bearing capacity of the pile is proportional to the outer diameter of the pile.

In conventional cast-in-place reinforced concrete piles, in order to fully utilize the concrete strength and increase the bearing capacity, it is often practiced to double the bottom of the pile tips.

Also, considering the case where the horizontal force due to the earthquake acts on the pile head,
In order to withstand the bending moment generated by this, the pile head is also expanded in diameter.

[Problems to be Solved by the Invention] In the above conventional cast-in-place pile, if the tip of the pile is doubled to increase the supporting force of the pile, the vertical load always supported by the pile increases. Since the horizontal force on the pile head used for seismic design is almost always represented by the product of vertical load and horizontal seismic intensity, the horizontal force also increases as the vertical load increases.
In order for the pile head to withstand the bending moment due to the increased horizontal force, it is often necessary to further expand the pile head. If the diameter of the head expansion is further increased in this way, the bending rigidity of the head of the pile becomes large, so that there is a disadvantage that a vicious cycle occurs in which the bending moment of the head of the pile due to ground displacement becomes larger.

This invention was made in order to solve such disadvantages, while increasing the supporting force without expanding the pile tip, and also a method of expanding a circular arc pile and a circular arc pile that can withstand the horizontal force due to ground displacement. It is intended to be provided.

[Means for Solving the Problem] In the expanded circular arc pile according to the present invention, the head of the pile formed in an arc shape having a radius of almost the same length as the vertical length up to the tip of the pile is expanded with steel pipe and concrete. It is characterized by

In addition, the method of expanding the circular arc pile is to insert a steel pipe that forms an expanded head into the pile head after placing the circular arc pile, place concrete between the steel pipe and the circular arc pile, and then steel pipe after hardening the concrete. It is characterized in that the head of the circular arc pile is welded and integrated with an iron plate.

[Operation] In the present invention, by making the pile arc-shaped, the area of the portion of the support layer that receives the vertical ground reaction force is increased without increasing the pile tip portion to increase the ground reaction force. At the same time, the entire length of the pile is increased to increase the frictional force on the peripheral surface. Furthermore, by expanding the pile head of this circular arc pile with steel pipe and concrete, the horizontal force due to ground displacement is dealt with.

Further, a diameter-expanded portion is formed by a steel pipe and concrete on the pile head of the arc-shaped pile, and the steel pipe of the diameter-expansion portion and the arc-shaped pile are welded and integrated with an iron plate to expand the pile head of the arc-shaped pile.

[Embodiment] FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention. As shown in the figure, the ground with the support layer 2 with N = 50 under the silt layer 1 with N = 10 and depth L ₁ (m) has a shaft diameter D (mm) and a vertical length to the tip. Radius R (m) of almost the same length as length L
The case where an arc-shaped cast-in-place pile (hereinafter referred to as an arc pile) 3 is embedded in the support layer 2 by L ₂ (m) is shown. Arc pile 3
Is made up of, for example, a steel pipe 4 and concrete 5 cast into the steel pipe 4, and the expanded head 6 of diameter D ₁ (mm) is formed at the pile steel pipe 7 and concrete 8 at the pile head of this circular arc pile 3. .

Hereinafter, according to this embodiment, the advantage of the supporting force by using the circular arc pile 3 will be described first, and then the advantage of providing the expanding portion 6 will be described.

The ultimate bearing capacity R _U (tf) of the circular arc pile 3 is determined by the sum of the pile tip resistance, the peripheral frictional force, and the upward ground reaction force, and is expressed by the following equation (1).

R _U = q _d · A + UΣL _i · f _i + Q _z (1) where A: pile tip area (m ² ) q _d : ultimate bearing capacity of pile tip (tf / m ² ) U: pile circumference Length (m) L _i : Pile length [m] on which the peripheral frictional force acts [m] f _i : Maximum peripheral frictional force of the layer on which the peripheral frictional force acts (tf
/ m ² ) Q _z : Upward ground reaction force (tf) For example, the depth of the silt layer 1 is L ₁ = 27 (m), and the depth of rooting is L ₂
= 3 (m), nominal diameter 600A, that is, outer diameter D = 609.6 (m
m), and Da設concrete 5 inside the steel tube 4 having a thickness of 9.5 (mm), pile tip resistance q _d · A in the case of reclamation the arc of radius R = 30 arc pile 3 (m) is the support If the estimated value of q _d in layer 2 is 300, then q _d · A = 300 × (π / 4) × 0.6096 ² = 87.51 (tf).

In this case, the length L _1R of the circular pile 3 in the silt layer 1 is 33.
6 (m), the length L _2R in the support layer 2 is 13.5 (m), so the peripheral frictional force is UΣL _i · f _i = 0.609π {(33.6 × 0.1 × 10) + (13.5 × 0.1 × 50)} = 193.5 (tf).

Further, the upward ground reaction force Q _z acts on the entire arc pile 3, but the supporting layer 2 having a large vertical component force and an N value of 50 or more is used.
Considering only the part embedded in the ground, and considering the ground reaction force to be small, upward ground reaction force in the support layer 2
Q _z2 can be expressed by the following equation.

Q _z2 = L _2R · K _U · δ · D (2) where L _{2R is the} vertical ground reaction force (cm) K _{U is the} ground reaction force coefficient (Kg / cm ³ ) δ : Settlement amount (cm) D: Pile outside diameter (cm) where ground reaction force coefficient K _U = 1 (Kg / cm ³ ), settlement amount δ = 1
(Cm), Q _z2 = 82.2 (tf). Therefore, the ultimate bearing capacity R _U of the circular pile 3 is the sum of these, and R _U =
It becomes 363.2 (tf).

On the other hand, as shown in FIG. 2, considering the case that construct a Chokukui 21 on the same ground, ultimate bearing capacity R _U in vertical piles _{21, R U = q d · A} + UΣL i · f i = 167.9 (tf ) become.

That is, the ultimate bearing capacity R _U of the circular pile 3 is about twice that of the straight pile 21. Therefore, in order to obtain the same ultimate bearing capacity R _U , the number of piles can be reduced to half by using the circular arc piles 3.

Further, comparing the allowable pulling force P _U of the circular pile 3 and the straight pile 21, the allowable pulling force P _U is determined by the circumferential surface friction force UΣL _i · f _i ,
In the case of the straight pile 21, it is 80.39 (tf / piece), whereas in the case of the circular pile 3, it is 193.5 (tf / piece), and the allowable pull-out force P _U
In consideration of the above, the number of circular arc piles 3 can be reduced to less than half that of the straight piles 21.

In the case of the circular arc pile 3, the ground further resists the pulling-out of the pile, and thus the pulling-out force can be increased.

Considering the buckling of the circular arc pile 3, the buckling load N _cr is expressed by the following equation.

N _cr = m _c EI / (Rθ) ² ··· (3) where m _c is a value determined by the support conditions of the pile E: Young's modulus of the pile material I: Second moment of section of the pile Rθ: Buckling length Where m _c = 32, E = 2.1 × 10 ⁶ (Kg / cm ² ), I = π (D ⁴ −D
_in ⁴ ) / 64 (D _in : Steel pipe 4 inner diameter of arc pile 3), Buckling length R
When the length from the pile head to the pile bottom view is taken as θ, the buckling load of the circular arc pile 3 is N _cr = 244 (tf).

On the other hand, considering the safety factor of 3 for the allowable bearing force P _a of the circular-arc pile 3, the ultimate bearing force R _{U changes} to R _a = R _U / 3 = 121 (tf), and the buckling load N _cr = 244 (tf It is about 1/2 of that of () and there is no risk of out-of-plane buckling. In the actual case, the circular arc pile 3
The buckling load N _cr is much larger than that obtained by the above model because all directions are constrained.

Next, the nominal diameter 800A, that is, the outer diameter D ₁ is 81
The improvement of the cross-sectional performance when the expanded head portion 6 is formed of the mouth steel pipe 7 of 2.8 (mm) and the thickness of 9 (mm) and the concrete 8 will be described.

Here, in consideration of the effect of the cross-section enhancement by the concrete 8, the steel pipe 4 and the pipe steel pipe 7 of the circular arc pile 3 are considered as stacked beams.
The improvement of the sectional performance in this case can be considered as the sum of the sectional moment of inertia of the steel pipe 4 and the sectional moment of inertia of the neck steel pipe 7.

Moment of inertia of area of _{600 A} , steel pipe 4 with a thickness of 9.5 (mm) I ₆₀₀
Is as follows.

I ₆₀₀ = π (D ⁴ -D _in ⁴ ) / 64 = π (60.96 ⁴ −59.06 ⁴ ) / 64 = 80593 (cm ⁴ ) The second moment of area I ₈₀₀ of the ₈₀₀ A mouth steel tube is I ₈₀₀ = π ( D ₁ ⁴ −D _1in ⁴ ) / 64 = π (81.28 ⁴ −79.48 ⁴ ) / 64 = 183356 (cm ⁴ ).

Therefore, the combined moment of inertia I _{w of} the expanded portion 6
Is I _w = I ₆₀₀ + I ₈₀₀ = 263949 (cm ⁴ ), and by expanding the pile head of the circular arc pile 3 by about 30% in diameter, bending rigidity (longitudinal elastic modulus × The second moment of area) can be approximately tripled as compared with the case of only the circular arc pile 3, and even if the number of piles is reduced, it is possible to sufficiently cope with the horizontal force.

Next, an example of a construction method of the circular arc pile 3 will be described.

For the construction of the circular arc pile 3, for example, as shown in FIG. 3, a tip drive type drill attached to the tip of the inner pipe 11 curved in the longitudinal direction.
Use 12

The tip drive type drill 12 comprises a guide portion 13 and a rotating portion 14 attached to the tip portion of the guide portion 13. The rotating portion 14 has a pilot bit 15 at the tip and is raised at a plurality of positions on the circumferential side surface. It has a retractable retract bit 16.

Then, while guiding the guide portion 13 of the tip drive type drill 12 on the inner surface of the steel pipe 4 which is curved in an arc shape having the radius R of the arc pile 3, the rotating portion 14 is projected from the tip of the steel pipe 4, and the pilot bit 15 and the retract. The inner pipe 11 and the steel pipe 4 are propelled while excavating the underground with the bit 16. Excavation water used for this excavation is supplied to the front surface of the pilot bit 15 through the inner pipe 11, and is discharged through the space between the inner pipe 11 and the steel pipe 4, which contains the waste sludge.

After excavating the ground in this way and installing the steel pipe 4 at a predetermined position, the inner pipe 11 and the tip drive type drill 12 are pulled out, concrete is placed in the steel pipe 4, and the arc pile 3 is completed.

After that, as shown in FIG. 4, the mouth steel pipe 7 is installed on the pile head of the arc pile 3, the reinforcing bar cage 9 is inserted between the arc pile 3 and the mouth steel pipe 7, and then the concrete 8 is poured. . After the cast concrete 8 hardens, the steel pipe 4 of the circular arc pile 3
And the upper end of the steel pipe 7 is welded and fixed with an annular iron plate 10. In this way, the steel pipe 4 and the base steel pipe 7 can be easily integrated into the steel plate 10 and the concrete 8.

Further, since the expanding head 6 can be made into a completely integrated structure, it is possible to cope with the horizontal force due to the ground displacement without increasing the outer diameter D ₁ of the expanding head 6 so much.

In addition, in the said Example, although the case where the circular arc pile 3 was formed with the steel pipe concrete pile was demonstrated, even if the circular arc pile 3 is formed with a reinforced concrete pile, the same effect as the said Example can be produced.

[Effects of the Invention] As described above, the present invention increases the ground reaction force and the peripheral frictional force by forming the pile into an arc shape, thereby increasing the pile supporting force without expanding the pile tip portion. It can be increased and the number of piles can be significantly reduced.

Moreover, since the pile supporting force is increased without expanding the pile tip, the horizontal force applied to the pile head due to ground displacement can be suppressed to a relatively small level, and the pile tip of the circular arc pile is expanded. Thereby, even if the number of piles is reduced, the horizontal force applied to the pile heads can be sufficiently dealt with.

Further, by reducing the number of piles, the construction period can be shortened and the construction cost can be reduced.

Further, by forming a diameter-expanded portion with a steel pipe and concrete on the pile head of the arc-shaped pile and welding the steel pipe and the arc-shaped pile of the diameter-expanded portion with an iron plate, the arc-shaped pile and the diameter-expanded portion are reliably integrated be able to.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, (a) is a vertical sectional view of an arc pile, (b) is a distribution diagram of N values, and FIG. 2 (a) is a vertical sectional view of a straight pile, (b). Is a distribution diagram of N values, FIG. 3 is an explanatory view showing a state when the circular arc pile is installed, and FIG. 4 is a vertical cross-sectional view showing an enlarged head of the circular arc pile. 1 ... silt layer, 2 ... support layer, 3 ... arc pile, 4 ...
Steel pipe, 5,8 …… Concrete, 6 …… Expansion head, 7 …… Steel pipe, 9 …… Reinforcing cage, 10 …… Steel plate.

Claims (2)

[Claims] Claim: What is claimed is: 1. An expanded circular arc pile in which the head of the pile formed in an arc shape having a radius substantially the same as the vertical length to the tip of the pile is expanded with steel pipe and concrete. 2. A steel pipe forming an expanded head is inserted into the pile head after placing the circular-arc pile, concrete is placed between the steel pipe and the circular-arc pile, and the steel pipe and the circular arc are cured after hardening of the concrete. A method for expanding a circular arc pile, characterized in that the pile heads of the pile are welded together with an iron plate to be integrated.