JP2001098544A - Precast pipe and foundation pile structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance support force as a foundation pile structure two times or more a conventional one, to reduce a using quantity of a pile periphery fixing liquid, and to efficiently enhance the support force more then an upper pile having the same shaft diameter. SOLUTION: A shaft part 1 is formed so that an outer diameter gradually reduces in a tapered shape toward the lower end 3a (an outer diameter D2) from the upper end 2a (an outer diameter D1). A thickness of the shaft part 1 is formed in t1 on the upper end and t2 on the lower end (t1>t2), and the thickness gradually reduces over the total length (a). Annular ribs 10, 7 having an outer diameter DD1 (DD1>D1) are formed in a lower end part 3 of the shaft part 1. A PC steel bar 13 is embedded in an almost central position in the thickness of the shaft part 1 (c) (d). The outer diameter D1 and the thickness t1 of the upper end 2a are the same as an outer diameter D0, t0 of an upper pile 28 (b). With such constitution, this ready-made pile 18 is constituted (a). The ready-made pile 18 for connecting the upper pile 28 is embedded in a pile hole for forming an expansive bottom part so that the annular ribs 7, 10 are positioned in the expansive bottom part to form a foundation pile structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prefabricated pile and a foundation pile structure which are buried in a pile hole to constitute a foundation pile structure of a building.

[0002]

2. Description of the Related Art The following techniques have been proposed for a foundation pile having a projection which is embedded in a pile hole together with a filler such as cement milk and to which another ready-made pile can be connected.

[0003] "Foundation pile structure" (Japanese Patent Laid-Open No. 7-4883)
3) "Foundation pile structure" (JP-A-2-232416) "Connecting pile method for ready-made concrete piles" (JP-A-8-4)
1870)

[0004] These are all buried in straight pile holes filled with a filler such as cement milk. In relatively weak ground, the vertical bearing force is mainly due to the peripheral surface friction over the entire length of the lower nodal pile. The bending moment force was mainly shared by the upper cylindrical pile. These joint piles were actually used for buildings that did not require much vertical and horizontal bearing capacity. Therefore, application to a foundation pile structure of a building requiring a high bearing capacity and a high bending moment force has been difficult.

[0005]

SUMMARY OF THE INVENTION Among the above prior arts,
With the above structure, the pile hole is excavated slightly larger than the outer diameter of the protrusion of the ready-made pile, so when the upper pile with the same diameter as the shaft of the ready-made pile is connected, the side wall of the There is a problem that a large gap is formed between the pile and the surface of the pile, and the amount of the filler in the pile hole increases. In addition, since the outer diameter of the protrusion of the ready-made pile must be smaller than the diameter of the shaft of the pile hole, the diameter of the upper pile is smaller than the diameter of the shaft of the pile hole and the diameter of the shaft of the lower pile. Since it cannot be made large, there is a problem that the strength is insufficient when an excessive bending moment occurs during an earthquake or the like.

Further, in the case of the above structure, a dedicated joint (joint pipe) is used between the upper pile and the lower pile, so that the joint must be welded to both the upper pile and the lower pile. However, there is a problem in that the work becomes complicated twice, the construction is complicated, and the cost is increased.

[0007] In addition, the joint reduction rate must be increased in the design calculation due to the problem of joint strength.
In fact, it can only be used for foundation construction where the strength of the joints is relatively unimportant.

Further, in the above-described structure, since the connecting portion having a large diameter is provided at the upper end of the lower pile, the thickness of the shaft portion of the ready-made pile and the thickness of the connecting portion are formed to be constant in centrifugal molding. Therefore, there was a problem that it was not possible to secure uniform axial strength over the entire length of the ready-made pile.

In addition, in the above-mentioned structure, in addition to the difference in wall thickness between the shaft portion and the connecting portion of the ready-made pile, there is a connecting portion having a large diameter in the middle of the shaft portion. When the pre-stress is introduced, the main reinforcing bars (such as PC steel bars) to be buried cannot be placed evenly in the center of the wall thickness.
There was a problem that the amount of stress was not constant between the shaft portion and the connection portion, and the axial force of the ready-made pile was uneven. Therefore, when an excessive bending moment or a vertical load is applied, there is a problem that stress concentration occurs near the connecting portion having a large diameter and breakage is likely to occur near the shaft portion below the connecting portion.

Generally, each of the above structures has been proposed as an extension of the friction pile taking only the strength against the bending moment of the upper pile into consideration, and can withstand a high vertical load about twice or more that of the conventional support pile. It was difficult to realize a high support pile foundation structure that could be achieved from the technical design and economic aspects.

[0011]

According to the present invention, however, the shaft is formed so that the diameter is gradually reduced downward at least at the lower portion, and a projection is formed at a portion buried in the enlarged bottom portion, so that the ready-made pile is formed. The above-mentioned problem was solved because of the configuration or the basic structure.

That is, the present invention relates to a lower pile connected to an upper pile, and a prefabricated pile buried in a pile hole enlarged bottom portion.
The upper end connecting portion is formed with the same connecting diameter as the shaft diameter of the upper pile, and at least at the lower portion, a shaft portion is formed so as to gradually decrease in diameter downward, and a position including at least the lower end portion of the shaft portion. It is a ready-made pile characterized by forming a projection on the pile.

Another aspect of the present invention is a prefabricated pile embedded in a pile hole having an enlarged bottom portion, wherein at least a lower portion is formed with a shaft portion having a diameter gradually decreasing downward, and the prefabricated pile is formed. A prefabricated pile, wherein a protrusion is formed at a position including at least a lower end portion of the shaft portion in a portion embedded in the expanded bottom portion.

[0014] Further, in the above-mentioned both ready-made piles, the shaft portion is directed downward, and a step is provided so that the diameter is gradually reduced. Further, the projections are ring-shaped projections, and are ready-made piles formed to have a large diameter with the outer diameter directed downward. In addition, the projection is an annular projection, and is a ready-made pile formed with a small diameter with the outer diameter directed downward. Further, the projection is an annular projection, and is a ready-made pile having substantially the same outer diameter. In addition, the upper end connecting portion is a ready-made stake formed with substantially the same shaft thickness as the upper stake. In addition, this is a ready-made pile in which the main reinforcing bar in the axial direction is arranged at a substantially central position in the radial direction within the thickness over the entire length.

Further, according to the present invention, a pile hole having an enlarged bottom portion following a shaft portion is excavated, and soil cement obtained by stirring and mixing the cement milk and the excavated soil injected into the enlarged pile bottom portion and the shaft portion of the pile hole is filled. Or a foundation pile structure in which a ready-made pile is buried in a pile hole in which excavated soil has been replaced with cement milk, wherein the ready-made pile has a shaft having a diameter gradually reduced downward at least at a lower part thereof. A portion is formed, and at least a lower end portion of the shaft portion is provided with a protrusion,
This is a foundation pile structure, wherein the protruding portion of the ready-made pile is embedded in the expanded bottom portion. Further, the ready-made pile has a structure in which one or a plurality of upper piles and a lower pile are connected, and the lower pile is formed at least at its lower part with a shaft portion so as to gradually decrease in diameter downward. And a projecting portion formed at least at a lower end portion of the shaft portion, and the upper pile is formed to have substantially the same diameter as an upper end connecting diameter of the lower pile.

The term "gradually smaller diameter" in the above includes any of a case where the diameter is continuously reduced in a tapered shape, a case where the diameter is reduced by providing a step-like step, and a case where the diameter is reduced by a combination thereof. .

In addition, the term "slower diameter gradually downward" in the above does not mean that the diameter is gradually reduced over the entire length of the ready-made pile, but at least the lower side of the ready-made pile is gradually reduced in diameter downward. If so, the shape of the upper part and the middle part is arbitrary, and may be straight, downward, small or large, or a combination thereof. This structure can be appropriately selected depending on the conditions of the supporting ground where the ready-made piles are embedded and the ground at each depth.

The above-mentioned "forming a projection at a position including at least the lower end of the shaft" means that one projection is formed at the lower end of the shaft and, if necessary, at another arbitrary position (the lower end,
It refers to a structure in which one or a plurality of protrusions are formed at an intermediate portion or an upper end portion.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In a ready-made pile 18 of the present invention, protrusions 7, 10 (annular ribs) are embedded in an enlarged bottom portion 22 of a pile hole 20, and are used for stiffening a root to exhibit a so-called high supporting force. It is a ready-made pile, so that the diameter gradually decreases downward,
The shaft 1 is formed, and a projection is provided at least at the lower end of the shaft 1.

The pile hole 20 in which the ready-made pile 18 is buried is
An enlarged bottom portion 22 having a large diameter at the lower end of 1 is formed. Inject cement milk into the pile hole 20 and agitate it with the excavated soil to make soil cement. Or, if necessary, to minimize the incorporation of silt or the like that is not good in strength quality, Has been replaced.

When the ready-made pile 18 is buried in the pile hole 20 and the projections 7 and 10 (annular ribs) of the ready-made pile 18 are located in the expanded bottom portion 22, the basic pile structure 30 of the present invention can be constructed. . In the foundation pile structure 30, the shaft portion 1 and the protrusions 7, 10 (annular ribs) of the ready-made pile 18 whose diameter gradually decreases downward.
Are located in the enlarged bottom portion 22 of the pile hole 20.

In the foundation pile structure 30 thus constructed,
Means that when a vertical load P occurs, the stress
Pile hole bottom direction V₁ And the angle V from the lower surface of each projection_Two To
Acts toward. Further, the shaft portion 1 gradually decreases downward.
Since it is formed in a tapered shape with a diameter, from the shaft surface
Stress V diagonally downward_Three Is propagated. Where V₁ , V_Two ,
V_Three Is the direction in which the vertical load P propagates.
The direction of the supporting force is V ₁ , V_Two , V_Three On the contrary, on
Acts upward and diagonally outward. At this time,
Power is S₁ , S_Two , S_Three The lower end of the ready-made pile 18
Conical shape on the lower edge of the raised part (angle of about 30 ° with vertical)
Propagates toward the pile hole bottom 23 and corresponds to the conical bottom surface.
A supporting pressure is generated at the portion where the pressure changes (FIG. 8A). Therefore, ready-made
The stress transmitted at the lower end of the pile 18 is dispersed in various directions.
Therefore, not only the protrusions 7 and 10 (annular ribs) but also the shaft 1
The structure also effectively utilizes the peripheral surface of the tapered portion.

The ready-made pile 18 of the present invention may be a single pile or a connection pile. In the case of a single pile,
The portion of the pile hole 20 located at the enlarged bottom portion 22 has a structure in which the shaft portion is gradually tapered downward and has a tapered shape and a projection is provided. When the connection pile is used, the upper pile 28a,
The lower pile connected to 28b,... And the lower pile 22 (usually the lowermost pile located at the lowermost end) is formed into a tapered shape by gradually reducing the diameter of the shaft part downward. Then, a projection is provided ".

In the case of a connection pile, the upper end connection portion 15 is formed with the same connection diameter as the shaft diameter of the upper pile 28b. If the depth is about the depth of the bottom of the pile hole (consolidation portion), the configuration can be made relatively short, and the range of use of the upper pile to be connected is expanded. For example, it is possible to select and use the upper piles 28a, 28b,... According to a change in the stratum up to the surface of the ground, and to select a structurally and economically optimum foundation pile structure (FIG. 8B). Further, since the lower pile 18 can be manufactured short, the weight can be reduced, and the shape and dimensions can be standardized as a ready-made pile dedicated to the bolster portion, and mass production becomes possible. In addition, since there are protrusions, they are generally easily damaged during transportation, etc., but because they can be manufactured with short dimensions, damage during handling during transportation and construction can be reduced, and if a plurality of protrusions are provided, stability increases, Furthermore, it leads to damage prevention.

[0025]

Embodiment 1 An embodiment of the present invention will be described with reference to FIGS.

An upper connecting end plate made of metal is provided on the upper end 2a of the shaft portion 1.
15, the shaft portion 1 has an upper end 2a (ie, an upper connecting end plate).
15) Outer diameter D₁ The lower end 3a (ie, the lower connecting end plate 1)
The outer diameter of 6) is D_Two Formed from the upper end 2a to the lower end 3a
Outer diameter gradually decreases continuously (tapered)
Is formed. Further, the thickness of the shaft portion 1 is the upper end t.₁ , Lower end t
_Two Formed by t₁ > T_Two Then, from the upper end 2a to the lower end 3a
In a tapered shape over the entire length of the
Is becoming The inner diameter of the hollow portion 5 is the upper end 2a.
D₁₁, D at the lower end 3a_{twenty two}Formed, gradually reduced in diameter
(FIG. 1A).

Annular ribs 10 and 7 are formed on the lower end 3 and the intermediate part 4 of the shaft 1, respectively. The outer diameters of the annular ribs 10 and 7 are DD ₁ (DD ₁ > D ₁ ) and are formed in the same manner.
The upper and lower edges 9 of the annular rib 10 are formed with slopes 11 and 12 extending to the outer wall of the shaft 1.

PC steel bars (main reinforcing bars) 13, 13 are buried along the annular shape at equal intervals in the thickness of the shaft portion 1 at substantially the center in the radial direction over the entire length (FIG. 1 ( c)
(D)). That is, the interval between the adjacent PC steel bars 13, 13 is formed narrower downward. The PC steel rod 1
Reinforcing reinforcing bars 14, 14 are helically embedded on the outer circumferences of the reinforcing bars 3, 13.

The outer diameter D ₁ and the wall thickness t of the upper connecting end plate 15
₁ is an upper pile 28 to be connected (an end plate 2 for connection of the upper pile 28).
The outer diameters D ₀ and t _{0 of} 9) are formed to be the same (FIG. 1B).

The shaft 1 and the annular projections 7, 10 as described above
In a predetermined formwork, a concrete cage is put in, a concrete is put, a prestress is introduced into the PC steel bar 14, and the concrete is integrally formed by centrifugal molding. (FIG. 1A).

Next, the use of the ready-made pile 18 of the present invention, that is, an embodiment of the foundation pile structure 30 will be described.

(1) The excavation rod 24 is rotated forward, the excavated soil is kneaded with the kneading drums 24a, 24a while the excavated soil is being kneaded on the pile hole wall, and a predetermined shaft portion 21 is excavated. When it reaches a predetermined supporting ground, the excavating rod 24 is rotated in the reverse direction to form the enlarged bottom portion 22 and the pile hole 20 including the shaft portion 21 and the enlarged bottom portion 22 is formed (FIG. 3A).

(2) During or after excavation, a consolidation liquid (cement milk) is injected into the expanded bottom portion 22 of the pile hole 20 to be stirred and kneaded with the excavated soil, or replaced with excavated soil. A root consolidation liquid layer 25 is formed. Similarly, a pile peripheral fixation liquid (cement milk) is injected into the shaft portion 21 of the pile hole 20, stirred and kneaded with the excavated soil, and the pile peripheral fixation liquid layer 26, which has been converted into soil cement almost to the pile hole mouth, is formed. Form (Fig. 3
(B)).

(3) Subsequently, the ready-made pile 18 of the present invention is used as the lower pile, and the connecting end plate 29 of the straight-shaped ready-made pile 28 is connected as the upper pile to the upper connecting end plate 15 of the ready-made pile 18. (FIG. 1B). The connection may be performed by means of welding or the like in the related art, and may be connected at the time of construction at the construction site or in advance at the factory or the like before construction. In addition, ready-made pile 28
Is arbitrary such as a so-called PHC pile, PRC pile, and SC pile.

The connected ready-made piles 18, 28 are rotated if necessary and lowered into the pile holes 20, and are buried with the annular ribs 7, 10 of the ready-made pile 18 positioned in the expanded bottom 22.
At this time, the ready-made pile 18 (lower pile) is easy to insert into the pile hole because the shaft portion 1 is formed to have a smaller diameter toward the lower side.

[0036] At this time, between the lower end 3a and Kuianasoko 23 off-the-shelf piles 18, for sagging straight load securing strength, providing a predetermined gap H _1. Furthermore, between the top surface X of拡底portion inside in the top 22 annular rib 7 and拡底portion 22 of the prefabricated pile 18, for scratch抜力ensuring strength, it is provided with a predetermined gap H _2. Then, both gaps H ₁ and H ₂ are also filled with soil cement or cement milk.

As described above, the foundation pile structure 30 is formed in a state where the root consolidation liquid layer 25 and the pile perimeter fixing liquid layer 26 are solidified together with the ready-made piles 18 and 28 (FIG. 3D).

(4) The outer diameter D ₁ and the thickness t ₁ of the upper connection end plate 15 are determined by the upper pile 28 (the connection end plate 2 of the upper pile 28) to be connected.
Since the outer diameters D ₀ and t _{0 of} 9) are formed to have the same dimensions, the proof stress against the bending moment can be improved, and the proof stress against the vertical load and the pull-out force can be improved. When a vertical load acts on the foundation pile structure 30 (the ready-made piles 28, 18), the foundation pile structure 30 has a lower surface 3a of the ready-made pile 18, a lower slope 12 of the annular rib 10, and a lower side of the annular rib 7. At the periphery of the slope 9, the shear force propagates in a conical shape (at an angle of about 30 ° with the vertical) toward the pile hole bottom 23 as shown by chain lines 32, 32 a, and 32 b, and the portion corresponding to the conical bottom surface A supporting force is generated at (Fig. 3
(D)). The vertical load acts on the entire inside of the expanded portion 22 of the foundation pile structure 30 because the integration between the annular ribs 7 and 10 and the solidified liquid layer 25 is high in the expanded portion 22 of the pile hole.

The foundation pile structure 30 (the ready-made piles 28, 1
8) When a pull-out stress acts on the annular ribs 7, 10
The shear force at the periphery of the upper slopes 8 and 11 is
a, 33b, conical shape (angle of about 30 ° with vertical)
And the pull-out resistance acts integrally with the ready-made pile 18 and the solidified solidification liquid layer 25 to form the expanded bottom portion 2.
2 (FIG. 3 (d)). The upper and lower spaces of the annular ribs 7 and 10 are arranged with a sufficient margin so that when a vertical load and a pulling force are applied to the ready-made pile, a supporting force based on the propagation of the shear force from the annular ribs 7 and 10 can be sufficiently generated. Have been.

(5) Another embodiment In the above embodiment, the outer diameter DD ₁ of the annular ribs 7 and 10 is different from that of the _first embodiment.
Is DD ₁ > D ₁ , but DD ₁ = D ₁ may be formed (FIG. 2C). In this case, the ready-made pile 1
8, since the upper end 2a of the shaft 1 has the maximum diameter, the excavation diameter of the shaft 21 of the pile hole 20 to be drilled is reduced, and the gap between the side wall of the shaft 21 and the outer wall of the ready-made pile 28 (upper pile). Can be narrowed, and the amount of fixation liquid used around the pile can be reduced.

Although the outer diameters of the plurality of annular ribs 7 and 10 are the same, they are formed so as to have a larger diameter downward (FIG. 2A). DD ₁ <the outer diameter DD _{2 of} the lower annular rib 10), or a smaller diameter can be formed downward (FIG. 2).
(B). Outer diameter DD ₂ of the outside diameter DD _1> lower annular rib 10 of the upper annular rib 7). Thus, when an excessive vertical load or pull-out force is applied, not only can the supporting force on the annular ribs 7 and 10 be increased, but even if the large-diameter annular rib which receives a relatively large force is broken first, the small-diameter annular rib is not affected. The annular rib does not break and plays a role of bearing.

Further, in the above embodiment, the annular rib 7,
Although the shaft 10 is formed integrally with the shaft 1, the shaft 10 can be joined as a separate member after the shaft 1 is formed (not shown). If a projection can be formed on the outer surface of the shaft portion, an intermittent projection (planar cross shape) or the like can be used instead of the annular ribs 7 and 10 (not shown).

Although two annular ribs 7 and 10 are provided,
The annular rib 10 can be further provided at the lower end to provide three annular ribs 6, 7, and 10 (FIG. 2C) or four or more annular ribs (not shown).
In this case, when the ready-made pile 18 is buried, if at least two of the annular ribs on the lower end side are located in the expanded bottom portion 21 of the pile hole 20, the upper annular rib is located in the shaft portion 21 of the pile hole 20. (Not shown).

It is desirable to provide a plurality of annular ribs located in the enlarged bottom portion 22 in consideration of the breakage of the annular ribs. However, if there is a sufficient margin in supporting strength, only one is provided. May be.

In the above embodiment, the outer diameter D ₁ and the thickness t ₁ of the upper connection end plate 15 are determined by the outer diameter D _{0 of the} upper pile 28 to be connected (the connection end plate 29 of the upper pile 28). , T ₀ , respectively, but the outer diameter D ₁ and the thickness t ₁ may be substantially the same as long as they can be connected to the connection end plate 29 of the upper pile 28.

In the above embodiment, the thickness of the shaft 1
Is the upper end 2a and the lower end 3a, t₁ > T_Two But t₁ 
<T_Two (Not shown). this
In this case, the wall thickness gradually changes from the upper end 2a to the lower end 3a.
And the PC steel bar is located at the center position in the radial direction in the wall thickness over the entire length.
Is buried in the place. Similarly, t₁ = T_Two , And
(Not shown). In short, the upper end 2 of the shaft 1 of the lower pile
Outer diameter D of a₁ , Wall thickness t ₁ Is the outer diameter D of the upper pile to be connected
₀ , Wall thickness t₀ It is sufficient if they are almost the same.

Further, in the above embodiment, the ready-made pile 18 is formed as a lower pile used as a connecting pile, but may be formed as a single pile integrated with the ready-made pile 28 (not shown).

Although a concrete pile is used in the above embodiment, a steel pipe pile having the same structure or a combination of these structures may be used (not shown).

[0049]

Based on the configuration of Experiment] Example 1, the shaft 1 of the prefabricated pile (lower _{pile) 18, D 1 = 700mm t} 1 = 100mm (D 11 = 500mm) D 2 = 600mm t 2 = 90mm (D ₂₂ = 420 mm). Further, an annular rib 7 and 10, when the distance from the bottom 3a and each _{L 1, L 2, DD 1} = DD 2 = 750mm, formed by _{L 1 = 1500mm L 2 = 500mm} . Further, the entire lower pile 18 has a concrete compressive strength of 1000 kg / cm ² .

The upper pile 28, the same 700m and an outer diameter D ₁
m, thickness, and inner diameter are 100 mm, the same as t ₁ and D ₁₁ , respectively.
It is set to 500 mm, and the whole concrete compressive strength is formed at 850 kg / cm ² .

Here, the concrete compression strength of the lower pile 18 and the upper pile 28 is varied for the purpose of keeping the axial strength of the pile constant. When the uniformity of strength is not required, the concrete compressive strength may be unified.

Further, in the ground having an average N value of 40 in the enlarged bottom 22, the pile hole 20 is excavated with the diameter of the shaft 21 being 780 mm and the diameter of the enlarged bottom 22 being 1100 mm (length 2500 mm).
Cement milk having a solidification strength of 300 kg / cm ² is injected into the pile hole expanded portion 22, stirred and mixed with the excavated soil, and turned into soil cement to form a root consolidation liquid. In addition, cement milk having a solidification strength of 200 kg / cm ² is poured into the pile hole shaft portion 21, and is stirred and mixed with excavated soil to form soil cement (strength of about 30 kg / cm ² ) to form a pile periphery fixing liquid. I have.

The upper pile 28 and the lower pile 18 are connected to form the
It is buried so that H ₁ = 500 mm and H ₂ = 500 mm within 0 to form a foundation pile structure 30.

In the foundation pile structure 30 constructed as described above, the vertical load resistance is 1000 kg / cm ² or more, and the pull-out force is 1
0 t / cm ² or more was confirmed, and the vertical load resistance and the pull-out resistance were significantly improved as compared with the conventional case.

[0055]

Embodiment 2 Another embodiment of the present invention will be described with reference to FIGS. In the first embodiment, the outer diameter of the ready-made pile 18 is D
From ₁ to D _2, it was continuously varied in a tapered shape,
In this embodiment, it is changed stepwise and intermittently.

The upper end 2a of the shaft portion 1 has an upper connecting end plate 15 made of metal, and the upper end portion 2 (the upper connecting end plate 15).
An outer diameter D ₁ of the the including), the outer diameter of the lower portion 3 (including a lower connecting end plate 16) is formed by D _2, the outer diameter of the intermediate section 4 D ₃
And the outer diameter is gradually reduced in a stepwise manner from the upper end 2a to the lower end 3a (D ₁ > D ₃ >).
D ₂ ).

The thickness of the shaft 1 is set at the upper end t ₁ and at the lower end t.
_2, is formed at an intermediate portion _{t 3, t 1> t 3} > t 2, in the form, the inner diameter of the hollow portion 5, D ₁₁ at the upper end, at D ₂₂ at the lower end,
D ₁₁ = D ₂₂ (FIG. 4A).

The lower end 3, the middle 4 and the upper end 2 of the shaft 1
The annular ribs 7 and 10 are formed on each of the steps. The outer diameter of the annular ribs 7 and 10 is DD ₁ (DD ₁ > D ₁ ),
The upper and lower edges of the annular rib 7 are formed with slopes 8 and 9 over the outer wall of the shaft 1, and the upper and lower edges of the annular rib 10 are formed with slopes 11 and 12 over the outer wall of the shaft 1.

Also, within the thickness of the shaft portion 1, PC steel bars (main reinforcing bars) 13, 13 are buried in an annular shape at equal intervals over the entire length (FIGS. 4 (a) and 4 (b)). By configuring the shaft section 1 in multiple stages, similarly to the first embodiment, the PC steel bars 13, 1
3 is disposed obliquely over substantially the entire length of the shaft portion 1 at a substantially central position in the wall thickness. Reinforcing reinforcing bars 14, 14 are helically embedded around the PC steel bars 13, 13 (FIG. 4 (b)).

The outer diameter D ₁ and the thickness t of the upper connecting end plate 15
Similarly to the first embodiment, 1 is formed to be the same as the outer diameters D ₀ and t ₀ of the upper pile 28 (the end plate 29 for connection) to be connected.

The structure of the shaft portion 1 and the annular projections 7 and 8 as described above is integrally formed of concrete to constitute the ready-made pile 18 of the present invention (FIG. 4A). In the above, for example, D ₁ = 700 mm, D ₃ = 650 mm, D ₂ = 60
0 mm, are formed in DD ₁ = 750 mm.

As in the second embodiment, if a step is provided in multiple stages and a shaft portion having a small diameter is formed downward, it is possible to cope with the manufacturing by partially shortening and extending the mold. Ready-made piles of various dimensions can be easily manufactured by attaching and removing the outer diameter formwork.

The ready-made pile 18 of the present invention based on the above embodiment
Is the same as in Example 1.

Next, another embodiment will be described.

In the above-described embodiment, an annular rib 17 is further provided on the lower end side of the lower end 3 of the shaft portion 1, and the lower end of the annular rib 17 is formed as a lower end 3a of the shaft portion 1 to form a bulging portion. An end plate 16 can also be provided (FIG. 6C). In this case, the outer diameter of the annular rib 17 is the outer diameter D of the upper end of the shaft portion 1.
Same as ₁ . By making the lower end of the pile bulge-shaped, the area of the lower end of the pile is increased, the integrity with the soil cement in the pile hole is improved, and the bearing capacity of the foundation pile structure is increased.

Further, a reinforcing bar can be arranged on the bulged portion, and more stable supporting force can be obtained. In addition, by making the outer diameter of the annular rib 17 in the shape of the bulging portion the same as the outer diameter of the upper end portion, the ready-made pile can be easily buried at a predetermined position in the pile hole, and the eccentricity of the foundation pile structure can be prevented.

Further, in the above embodiment, the annular rib 7,
10 have the same DD₁ But the outer diameter of the annular rib 7
To DD₁ The outer diameter of the annular rib 10 is DD_Two And DD₁ >
DD _Two (FIG. 6A). Also, DD
₁ <DD_Two The outer ends of the annular ribs 7 and 10 and the shaft
The upper end 2a of the part 1 should be on the same straight line (on the same cone).
(FIG. 6B). Due to these, excessive droop
When a direct load or pull-out force is applied, the annular ribs 7, 10
Not only increase the supporting pressure on
Even if the received large-diameter annular rib is damaged first, the small-diameter annular rib
The valve does not break, and serves as a bearing.

In the above embodiment, the annular rib 7 is provided on each step between the upper end portion 2, the intermediate portion 4, and the lower end portion 3 of the shaft portion 1.
10, the annular ribs 7 and 10 can be formed at the intermediate position of the upper end portion 2 of the shaft portion 1 and the intermediate position of the intermediate portion 4 of the shaft portion 1, respectively (FIG. 7). In this case, the steps 19a and 19b between the upper end 2, the middle 4 and the lower end 3 of the shaft 1 appear on the surface. Thereby, the stress applied to each step is dispersed, and damage due to concentration of the stress in the step can be prevented.

In the above embodiment, it is desirable that the PC steel rod 13 is obliquely buried in the shaft portion 1 and is located substantially at the center of the wall thickness over the entire length. or intensity is variable, by placing such reinforcing rebar (not shown) in the shaft portion 1 upper portion 2 of the wall thickness t _2, the PC steel bars 13, the thickness at the lower end 3 t
_{2 and} can be buried at the same position from the inner wall of the hollow portion 5 upward (FIG. 5).
(A) to (d)).

Other embodiments are the same as the first embodiment.

[0071]

According to the ready-made pile of the present invention, the upper end connecting portion is formed to have the same connecting diameter as the shaft diameter of the upper pile, and at least at the lower portion, the shaft portion is gradually reduced in diameter downward. Since it is formed, there is an effect that the vertical load or the like on the ready-made pile can be reliably transmitted to the lower pile hole bottom portion and the supporting ground without causing stress concentration at the connection portion.
In addition, since the upper end connection portion is formed with the same connection diameter as the shaft diameter of the upper pile, the supporting force can be increased, and the upper connection portion can be easily connected by the normal connection means of the upper and lower piles having the same diameter.

Further, since the shaft portion of the ready-made pile is formed in a tapered shape or a stepped shape so as to gradually decrease in diameter downward, the height (outer diameter) of the protrusion can be relatively increased.
Also, compared to the outer diameter of the ready-made pile, the gap with the shaft diameter of the drill hole to be drilled can be made smaller, the amount of pile hole filler such as cement milk is reduced, and the surface area of the pile hole expanded bottom is large. Since the projecting portions can be arranged, the integration at the pile hole expanded bottom portion is improved, and there is an effect that the supporting force of the entire foundation pile structure can be increased to twice or more the conventional one.

Further, since the shaft portion is formed so as to gradually become smaller in diameter, it can be easily lowered when buried in the pile hole, and the construction efficiency can be improved.

[Brief description of the drawings]

FIG. 1A is a front view of a first embodiment of the present invention, and FIG.
Is a schematic longitudinal sectional view of a state where the upper piles are joined, (c) is a sectional view taken along the line AA in (b), (d) is B in (b).
It is sectional drawing in the -B line.

FIGS. 2A, 2B and 2C are front views of another embodiment.

FIGS. 3A and 3B are longitudinal sectional views showing a construction process of a foundation pile structure using a ready-made pile of the present invention.

FIG. 4A is a front view of a second embodiment of the present invention, and FIG.
FIG. 3A is a cross-sectional view taken along line GG of FIG.

FIG. 5A is a front view of another embodiment of the present invention, and FIG. 5B is a cross-sectional view taken along line CC of FIG.
(C) is a sectional view taken along line EE of (a), and (d) is a sectional view taken along line FF of (a).

FIGS. 6A, 6B, and 6C are front views of another embodiment.

FIG. 7 is a front view of another embodiment.

FIG. 8 is a conceptual diagram of a ready-made pile or foundation pile structure of the present invention,
(A) shows the propagation of the stress in the pile hole expanded bottom, and (b) shows an example of the entire configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shaft part 2 Upper end part (shaft part) 2a Upper end (shaft part) 3 Lower end part (shaft part) 3a Lower end (shaft part) 4 Intermediate part (shaft part) 5 Hollow part (shaft part) 6 Annular rib 7 Annular rib 10 Annular rib 13 PC steel bar (main rebar) 14 Reinforcing bar 15 Upper connection end plate 16 Lower connection end plate 17 Annular rib 18 Ready-made pile (Lower pile) 19a, 19b Step 20 Pile hole 21 Pile hole shaft 22 Expanded bottom part of pile hole 23 Bottom of pile hole 25 Root fixation liquid layer 26 Pile perimeter fixed liquid layer 28 Upper pile (ready-made pile) 29 End plate of upper pile 30 Basic pile structure

Claims (10)

[Claims] 1. A lower pile connected to an upper pile, and in a ready-made pile embedded in a pile hole expanded bottom portion, an upper end connecting portion is formed to have the same connecting diameter as a shaft diameter of the upper pile, and at least a lower portion is formed. A prefabricated pile, wherein a shaft portion is formed so as to gradually decrease in diameter downward, and a projection is formed at a position including at least a lower end portion of the shaft portion. 2. A prefabricated pile embedded in a pile hole having an enlarged bottom portion, wherein at least a lower portion has a shaft portion formed so as to gradually decrease in diameter downward, and is formed in the enlarged bottom portion of the prefabricated pile. A ready-made pile, wherein a projection is formed at a position including at least a lower end portion of the shaft portion in a portion to be buried. 3. The device according to claim 1, wherein the shaft portion is directed downward, and a step is provided to gradually reduce the diameter.
Or the ready-made stake according to 2. 4. The ready-made pile according to claim 1, wherein the projection is an annular projection, and the outer diameter of the pile is formed to be large toward the bottom. 5. The prefabricated pile according to claim 1, wherein the projection is an annular projection, the outer diameter of which is formed to be smaller toward the lower side. 6. The ready-made pile according to claim 1, wherein the projections are annular projections and have substantially the same outer diameter. 7. The prefabricated pile according to claim 1, wherein the upper end connecting portion is formed to have substantially the same shaft thickness as the upper pile. 8. The prefabricated pile according to claim 1, wherein the main reinforcing bar in the axial direction is arranged at a substantially central position in the radial direction within the wall thickness over the entire length. 9. A pile hole having an enlarged bottom portion following a shaft portion is excavated, and soil cement obtained by stirring and mixing cement milk and excavated soil injected into the enlarged pile bottom portion and the pile hole shaft portion is filled or excavated. In a pile hole in which soil is replaced by cement milk, a foundation pile structure in which a ready-made pile is buried, wherein at least the lower part of the ready-made pile forms a shaft portion so that its diameter gradually decreases downward. And a projection provided at least at a lower end portion of the shaft portion, and the projection portion of the ready-made pile is embedded in the expanded bottom portion. 10. The ready-made pile has a structure in which one or a plurality of upper piles and a lower pile are connected to each other, and the lower pile is formed so that at least a lower part thereof has a shaft portion whose diameter gradually decreases downward. And a projecting portion is formed at least at a lower end portion of the shaft portion, and the upper pile is formed to have substantially the same diameter as an upper end connecting diameter of the lower pile.