JP2004011355A - Foundation pile with screw bit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foundation pile with a screw bit greatly enhancing the ability to support load, while keeping its manufacturing cost and weight from increasing. <P>SOLUTION: The screw bit having a length equal to one pitch of a screw is mounted on the outer peripheral surface of the lower end of a pile body formed of a steel pipe. The pile is characterized by having a reinforcing cylinder having a predetermined length and having its lower end face made to abut the radial mid portion of the upper surface of the screw bit, and a fixing means for fixing the reinforcing cylinder coaxially to the outer peripheral surface of the pile body. As the fixing means, a plurality of plate-or bar-shaped spacers are preferably securely fitted into a cylindrical space between the pile body and the reinforcing cylinder along its circumferential direction, with a predetermined space therebetween. Also, an auxiliary bit for assisting the screw bit in drilling is provided preferably to protrude downward from the lower surface of the screw bit. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a type in which a screw bit is attached to a lower end portion of a steel pipe pile main body and which is screwed into the ground while rotating the pile main body by a rotary drive device, to increase its load supporting function. The present invention relates to an improved foundation pile so that even if the outer diameter of the screw bit is increased, inconveniences such as a remarkable increase in manufacturing cost do not occur.
[0002]
[Prior art]
When the foundation pile provided with the above screw bit approaches a predetermined burial depth, a construction method is employed in which the cement milk is sprayed from the lower end of the pile and further excavated until the pile reaches the predetermined depth.
According to this method, the lower end of the laid foundation pile is wrapped in a hardened cementitious mass formed by hardening a mixture of the soil loosened by a screw bit and cement milk. (Refer to the symbol B in FIG. 5).
The outer diameter of this hardened mass is somewhat larger than the outer diameter of the screw bit, and the height dimension can be arbitrarily changed by adjusting the timing of starting the injection of cement milk.
In this way, by forming a hardened mass having a larger outer diameter at the lower end of the foundation pile in a fixed state, the pressure receiving bottom area of the foundation pile is increased, and the load bearing capacity of the foundation pile is correspondingly increased. Can be raised.
[0003]
[Problems to be solved by the invention]
The degree of improvement in the load bearing capacity of the foundation pile due to the formation of the hardened mass is substantially proportional to the area of the bottom area of the hardened mass.
Therefore, the load bearing capacity of the foundation pile can be increased as the outer diameter of the screw bit is increased.
[0004]
However, even if the outside diameter of the screw bit is increased without injecting the cement milk, a certain effect of improving the load bearing performance can be obtained.
Also, the load bearing capacity can be increased by increasing the outer diameter of the pile body.
[0005]
However, as the outer diameter of the screw bit is increased, the bending and acting force applied to the screw bit during excavation increases, and it is necessary to increase the thickness of the screw bit so as to withstand it.
Furthermore, if the thickness of the pile main body is not increased with the increase in the thickness of the screw bit, there is a risk that the essential pile main body will be buckled and deformed.
Therefore, as the outer diameter of the screw bit increases, the manufacturing cost increases and the foundation pile must be heavy.
The method of increasing the outer diameter of the pile body to improve the load bearing capacity is difficult to adopt from the viewpoint of cost effectiveness.
[0006]
Therefore, an object of the present invention is to devise a foundation pile having a screw bit, which can achieve a great improvement in load bearing capacity while minimizing an increase in manufacturing cost and weight.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a foundation pile with a screw bit according to the present invention is
In the case where the screw bit of the length of one pitch of the screw is attached to the outer peripheral surface of the lower end of the steel pipe pile body,
With the outer diameter of each of the pile main body and the screw bit, the reinforcing cylinder of an appropriate length having an intermediate size outer diameter, coaxial with the pile main body with its lower end abutting on the upper surface side of the screw bit It is characterized by being fixed to.
Then, a plurality of plate-like or rod-like spacers may be fixedly inserted into the cylindrical gap between the pile body and the reinforcing cylinder at equal intervals in the circumferential direction of the cylinder.
Further, an auxiliary bit for assisting the excavation may be provided to project downward from the lower surface of the screw bit.
The auxiliary bit may be formed at a portion where the lower end of the spacer penetrates through the lower surface of the screw bit.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a partially broken side view showing a main portion (lower end portion) of a foundation pile A of this embodiment, and FIG. 2 is a top view thereof.
[0009]
A screw bit 2 having a length corresponding to one pitch of the screw is attached to the outer peripheral surface of the lower end portion of the steel pipe pile body 1 of the foundation pile A.
As shown in the plan view of FIG. 3, the screw bit 2 is divided into two divided bits 2A and 2B each having a length corresponding to a half pitch.
[0010]
As shown in FIG. 1, the two divided bits 2A and 2B are welded to the outer peripheral surface of the pile main body 1 in a state of crossing in an X shape when viewed from the side.
Further, as shown in FIG. 3, each of the divided bits 2 </ b> A, 2 </ b> B is inclined at a predetermined angle with respect to the direction of the cutting edge a formed on the inclined lower edge and the radial direction of the pile body 1.
[0011]
At the lower end of the pile main body 1, as shown in FIGS. 1 and 2, small plate-shaped tip bits 3 shown in FIG. It protrudes downward.
Although not shown, the open lower end of the pile body 1 is closed by a plug having a discharge port for cement milk.
[0012]
On the upper surface side of the screw bit 2, a reinforcing cylinder 4 for receiving a bending action force exerted on the screw bit 2 during excavation of the foundation pile A, the lower end surface of which is brought into contact with the upper surface of the screw bit 2. In this state, it is fixed to the pile main body 1 coaxially.
As shown in FIGS. 1 and 2, the outer diameter of the reinforcing cylinder 4 is such that the lower end surface thereof can be brought into contact with an intermediate portion in the radial direction (width direction) of the screw bit 2.
The length of the reinforcing cylinder 4 may be set to an appropriate length that can reliably receive the bending action.
[0013]
In order to fix the reinforcing cylinder 4 to the pile main body 1 coaxially, in this embodiment, as shown in FIGS. 1 and 2, a cylindrical gap b between the pile main body 1 and the reinforcing cylinder 4 A method is adopted in which four strip-shaped spacers 5 are inserted at equal intervals in the circumferential direction of the cylinder and then welded to the pile body 1, the screw bit 2, and the reinforcing cylinder 4, respectively.
[0014]
As shown in FIG. 4A, the two spacers 5, 5 which are opposed to each other among the four spacers 5 are provided at the lower end thereof to assist the excavation of the screw bit 2. The auxiliary bit 5A is formed.
The portion of the auxiliary bit 5A protrudes below the screw bit 2 through a notch c (see FIG. 3) provided in the divided bits 2A and 2B.
The auxiliary bit 5A may be made separately from the spacer 5 and welded to an appropriate position below the screw bit 2.
[0015]
Next, the operation of the foundation pile A will be described.
First, a self-propelled pile burying machine (not shown) is transported to a construction site.
A rotating drive device for rotating the foundation pile A in a suspended state is mounted on the pile support pole erected on the pile burying machine so as to be vertically movable.
Then, the top end of the foundation pile A is connected to this rotary drive device, and the lower end is grounded to a predetermined position on the ground to be buried.
[0016]
Then, when the rotary drive is started, first, the tip bit 3 starts excavating the ground.
Subsequently, the auxiliary bit 5A located immediately above the tip bit 3 excavates a wider area and plays a leading role in reducing the excavation resistance of the screw bit 2 having a large outer diameter.
[0017]
Following the auxiliary bit 5A, the leading screw bit 2 also starts excavating.
The outer diameter of the screw bit 2 is considerably larger than that of a conventional foundation pile of the same kind.
To that extent, the excavation resistance exerted on the screw bit 2 becomes larger.
[0018]
In order to prevent the screw bit 2 from bending and deforming due to the increased excavation resistance, the lower end surface of the reinforcing cylinder 4 is provided at a radially intermediate position on the upper surface side of the screw bit 2 over the entire circumference thereof. Have been abutted.
Therefore, of the entire area of the screw bit 2, the part that substantially receives the bending action force is limited to only the portion protruding outside the reinforcing cylinder 4.
[0019]
Therefore, when the outer diameter of the screw bit is increased in order to increase the load bearing capacity of the foundation pile, as described at the beginning, it is necessary to increase the thickness of the screw bit as a measure to prevent its bending deformation. Disappears.
As described above, if the thickness of the screw bit is increased, the thickness of the pile body as the mounting base must also be increased.
Therefore, the weight of the foundation pile and the production cost are greatly increased.
[0020]
With the excavation of the foundation pile A, the portion of the screw bit 2 excavated around the pile body 1 is backfilled by the surrounding earth pressure after passing through the screw bit 2.
[0021]
When the lower end of the foundation pile A reaches near a predetermined depth, the cement milk pumping device (not shown) mounted on the self-propelled pile burying machine is operated to be incorporated into the lower end of the pile body 1. The excavation is further continued while the cement milk is ejected from a certain ejection nozzle (not shown), and when the cement milk reaches a predetermined depth, the excavation and the ejection are stopped.
During this time, the cement milk is mixed with the soil excavated by the screw bit 2, the tip bit 3, and the auxiliary bit 5A.
[0022]
When the mixture has hardened, as shown in FIG. 5, a hardened cementitious mass B wraps the lower end of the foundation pile A in a fixed state.
Since the cement milk somewhat penetrates outside the excavation area, as described above, the diameter of the hardened mass B is larger than the outer diameter of the screw bit 2.
Then, the height of the hardened mass B is substantially equal to the excavation distance of the foundation pile A after the start of the injection of the cement milk.
[0023]
【The invention's effect】
As is apparent from the above description, the use of the foundation pile provided with the screw bit according to the present invention provides more practical effects as listed below as compared with conventional foundation piles of the same type.
(A) Even if the outer diameter of the screw bit is increased in order to increase the load bearing capacity of the foundation pile, the reinforcing cylinder prevents its bending deformation, so that it is not necessary to increase the thickness of the screw bit. .
(B) If the thickness of the screw bit is increased, it is necessary to correspondingly increase the thickness and thickness of the pile body. Extremely large, including the effect of suppressing the weight of piles.
(C) Even if the outer diameter of the screw bit is increased, the auxiliary bit provided on the lower surface of the screw bit eases the excavation resistance.
[Brief description of the drawings]
FIG. 1, showing one embodiment of the present invention, is a partially broken side view of a lower end portion of a foundation pile.
FIG. 2 is a top view of FIG.
FIG. 3 is a plan view of a divided bit according to the first embodiment;
FIG. 4 is a perspective view of a spacer and a tip bit according to the first embodiment;
FIG. 5 is a partial longitudinal sectional view showing a state in which a cementitious hardened mass is formed at the lower end of the buried foundation pile.
[Explanation of symbols]
A Foundation pile B Hardened lump 1 Pile body 2 Screw bit 2A, 2B Split bit 3 Tip bit 4 Reinforcement cylinder 5 Spacer 5A Auxiliary bit a Cutting edge b Cylindrical gap c Notch

Claims (4)

In the case where the screw bit of the length of one pitch of the screw is attached to the outer peripheral surface of the lower end of the steel pipe pile body,
With the outer diameter of each of the pile main body and the screw bit, the reinforcing cylinder of an appropriate length having an intermediate size outer diameter, coaxial with the pile main body with its lower end abutting on the upper surface side of the screw bit A foundation pile equipped with a screw bit, which is fixed to the base. 2. A plurality of plate-shaped or rod-shaped spacers are fitted in a cylindrical space between the pile main body and the reinforcing cylinder in a fixed state at equal intervals in the circumferential direction of the cylinder. Foundation pile with screw bit. 2. A foundation pile provided with a screw bit according to claim 1, wherein an auxiliary bit for assisting the excavation movement is protruded downward from a lower surface side of the screw bit. The foundation pile provided with a screw bit according to claim 3, wherein the auxiliary bit is formed at a portion where a lower end portion of the spacer penetrates a lower surface of the screw bit.

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