JP7186317B2 - Construction method of cast-in-place concrete pile and cast-in-place concrete pile - Google Patents

Description

The present invention relates to a method for constructing a cast-in-place concrete pile and a cast-in-place concrete pile.

Conventionally, cast-in-place concrete expanded-bottom piles have been widely used as pile foundations for heavy buildings such as skyscrapers.

A cast-in-place concrete expanded bottom pile (cast-in-place concrete pile) has a substantially constant diameter shaft and a substantially truncated cone-shaped expanded bottom formed by expanding the tip of the shaft according to the required bearing capacity. By providing an enlarged bottom portion at the tip of the pile, the bearing strength can be greatly improved (see, for example, Patent Document 1).

When constructing a cast-in-place concrete expanded bottom pile, for example, an excavator is used to excavate and form an excavation hole having a substantially constant diameter from the ground surface to a predetermined depth while being filled with a stabilizing liquid. Next, at the stage where a bottom-enlarging excavator (bottom-enlarging machine such as a bottom-enlarging bucket) connected to the tip of the rod is inserted and placed at the tip of the excavation hole, the rod is rotated around the central axis while expanding the excavator for bottom-enlarging. Rotate to excavate the ground of the hole wall portion and widen the tip of the excavated hole. Then, a reinforcing bar cage is built into the expanded excavation hole, and concrete is poured using a tremie pipe to replace the stabilizing liquid, and if necessary, the pile head side is backfilled or the pile head foundation is constructed. And so on, the construction of the cast-in-place concrete expanded bottom pile is completed.

Japanese Patent No. 4120478

Here, when constructing a plurality of bottom-enlarged piles 1, the pile interval between adjacent bottom-enlarged piles 1 is generally (shaft diameter (average diameter of shaft portion 2) + bottom-enlarged diameter (average diameter of bottom-enlarged portion 3)) or more. .

On the other hand, as shown in FIG. 9, due to the design, there may be a portion where the interval between the pillars 5 of the building body 4 (=the interval between the piles 1) is narrower than the expanded bottom diameter. Therefore, as shown in FIG. The enlarged bottom portion 3 of the enlarged bottom pile 1 is shifted vertically (up and down) so that the enlarged bottom portion 3 does not overlap.

However, if the adjacent bottom-enlarged piles 1 are shifted in a plane, the position of the pillar 5 of the building body 4 and the position of the pile 1 are deviated, resulting in a large moment being generated in the bottom-enlarged pile 1. Therefore, it is necessary to thicken the base 7 (Fig. 10).

In addition, if the expanded bottom portion 3 of the adjacent expanded bottom pile 1 is shifted in the vertical direction, the excavation of the lower pile 1 will be performed directly below the upper pile bottom 1a. As a result, the load P of the upper pile 1 is transmitted to the lower pile 1, which may lead to insufficient bearing capacity of the lower pile 1 (Fig. 11).

On the other hand, as shown in FIG. 12, the excavation holes of the adjacent enlarged bottom piles (enlarged bottom pile portions) 1 are excavated and formed at intervals such that at least the shaft portions 2 do not overlap, and the ground between the excavated holes of the adjacent enlarged bottom piles 1 is formed. are excavated and two adjacent bottom-enlarged pile portions (1) are connected by a wall portion 14 to construct one bottom-enlarged pile 1 (see, for example, Patent Document 1).

However, as shown in FIG. 13, when excavating the connecting pile portion 8, the excavator 9 bends toward the excavation hole 10 side of the expanded bottom pile portion (1) excavated in advance (the excavation direction is shifted), There is a possibility that the ground G of the connection pile portion 8 cannot be excavated appropriately.

On the other hand, if the ground G of the connecting pile portion 8 between the excavation holes 10 of the adjacent enlarged bottom pile portions (1) is excavated by a machine for constructing a diaphragm wall, the connecting pile portion 8 can be formed without bending the excavation hole. Excavation work can be performed.

However, since the excavator for pile 1 (earth drill, etc.) and the excavator for the diaphragm wall (reverse, etc.) are different machines, it is necessary to bring two types of large dedicated machines to the site. Working with a wall excavator is expensive and requires a large area for ancillary equipment, making the total cost to construct the pile 1 very high. Moreover, the space required for construction is also very large.

In view of the above circumstances, the present invention makes it possible to excavate and form excavation holes of adjacent expanded bottom pile portions and connecting pile portions with the same excavator, efficiently and economically from a plurality of expanded bottom pile portions and connecting pile portions. To provide a cast-in-place concrete pile construction method and a cast-in-place concrete pile capable of constructing a wide-bottomed pile.

In order to achieve the above objects, the present invention provides the following means.

The method for constructing a cast-in-place concrete pile of the present invention includes an enlarged bottom pile portion consisting of a cylindrical shaft portion and a substantially truncated cone-shaped enlarged bottom portion formed by expanding the tip portion of the shaft portion, and is provided at a predetermined interval. A method for constructing a cast-in-place concrete pile comprising a connecting pile portion that connects the adjacent enlarged bottom pile portions, wherein the ground of a pair of adjacent enlarged bottom pile portions or the ground of the connecting pile portion is improved. A ground improvement step of forming a columnar soil improvement body, and the ground of the connected pile portion that does not form the ground improvement body, or the ground of the pair of adjacent enlarged bottom pile portions, is excavated by an excavator for piles. A preceding excavation step of forming an excavation hole by pre-excavating using and the ground of the adjacent pair of enlarged bottom pile portions forming the soil improvement body, or the ground of the connecting pile portion, using an excavator for piles a subsequent excavation step of forming a cylindrical excavation hole by following excavation while guiding in the vertical direction with the soil improvement body, and forming a connected excavation hole by communicating with the excavation hole formed by the preceding excavation; and a concrete placing step of placing concrete in the interconnected excavated holes formed by the excavated holes of the adjacent enlarged bottom pile portions and the excavated holes of the connecting pile portions.

In the cast-in-place concrete pile construction method of the present invention, in the trailing excavation step, the tip of the excavator for piles is coaxial with the central axis of the excavator for piles and protrudes below the excavation blade. A stabilizer, which is a positioning/guide convex portion, is provided, and the stabilizer is pierced into the soil improvement body, so that trailing excavation can be performed while guiding the excavator for piles in the vertical direction by the soil improvement body and the stabilizer. desirable.

In the construction method of the cast-in-place concrete pile of the present invention, in the ground improvement step, it is more desirable to form the ground improvement body so that the compressive strength is increased by the ground improvement.

In the method for constructing cast-in-place concrete piles of the present invention, in the ground improvement step, in a plan view, another straight line that is orthogonal to a straight line that connects the central axis of the pair of adjacent enlarged bottom pile portions and the central axis of the connecting pile portion A plurality of the ground improvement bodies may be arranged side by side.

In the method for constructing cast-in-place concrete piles of the present invention, in the ground improvement step, the ground on the central axis of the pair of adjacent enlarged bottom pile portions or the ground on the central axis of the connecting pile portion is improved. forming an improvement body, drilling the soil improvement body on the central axis to form a guide hole extending in the vertical direction in the soil improvement body, and engaging the stabilizer with the guide hole in the trailing excavation step; The pile excavator may be guided in the vertical direction by following excavation while the piles are aligned.

The cast-in-place concrete pile of the present invention includes an enlarged bottom pile portion composed of a cylindrical shaft portion and a substantially truncated cone-shaped enlarged bottom portion formed by expanding the tip of the shaft portion, and an adjacent pile portion provided at a predetermined interval. A cast-in-place concrete pile provided with a columnar connection pile portion that connects the enlarged bottom pile portions that meet, wherein the axial connection is formed by integrally connecting the shaft portions of the adjacent pair of the enlarged bottom pile portions and the connection pile portion. One side surface and the other side surface of the portion are formed to have an arc uneven shape in which at least three convex arc surfaces extending from the upper end to the lower end of the shaft connecting portion are arranged in parallel.

According to the cast-in-place concrete pile construction method and cast-in-place concrete pile of the present invention, it is possible to excavate and form the excavation holes of the adjacent enlarged bottom pile portion and the connecting pile portion with the same excavator, and it is possible to excavate and form a very large pile such as a skyscraper. It is possible to efficiently and economically construct a cast-in-place concrete expanded bottom pile with a high supporting strength that can suitably support the axial force of a column.

FIG. 4 is a diagram showing a procedure for excavating the ground between adjacent enlarged bottom pile portions in the cast-in-place concrete pile construction method according to the first embodiment of the present invention. FIG. 4 is a diagram showing a procedure for forming excavation holes in a pair of enlarged-bottom pile portions and an enlarged-bottom portion of a connecting pile portion in the method for constructing a cast-in-place concrete pile according to the first embodiment of the present invention. In the construction method of the cast-in-place concrete pile according to the first embodiment of the present invention, FIG. In the construction method of the cast-in-place concrete pile according to the first embodiment of the present invention, FIG. It is a figure which shows the cast-in-place concrete pile which concerns on 1st, 2nd embodiment of this invention. In the construction method of the cast-in-place concrete pile which concerns on 2nd Embodiment of this invention, it is a figure which shows the procedure which excavates the ground of the excavation hole of a connection pile part, and one expanded-bottom pile part. In the construction method of the cast-in-place concrete pile which concerns on 2nd Embodiment of this invention, it is a figure which shows the procedure which excavates the ground of the other expanded-bottom pile part. FIG. 10 is a diagram showing a procedure for forming excavation holes in a pair of enlarged-bottom pile portions and an enlarged-bottom portion of a connecting pile portion in a method for constructing a cast-in-place concrete pile according to a second embodiment of the present invention. It is a figure which shows the case where the space|interval (= space|interval of a pile) of the pillar of a building main body produced the part narrower than the diameter of an enlarged bottom. It is a figure which shows the state which shifted the position of the adjacent bottom expansion pile planarly. It is a figure which shows the state which shifted the bottom-enlarged part of the adjacent bottom-enlarged pile in the perpendicular direction. It is a figure which shows the state which connected two adjacent bottom-enlarged pile parts with a wall part, and constructed|assembled as one bottom-enlarged pile. It is a figure which shows the state which bending generate|occur|produced when excavating the ground between two adjacent bottom-enlarged pile parts.

Hereinafter, a method for constructing a cast-in-place concrete pile and a cast-in-place concrete pile according to a first embodiment of the present invention will be described with reference to FIGS.

In the construction method of the cast-in-place concrete pile of the present embodiment, as shown in FIGS. 2 and a substantially truncated cone-shaped enlarged bottom portion 3 formed by expanding the tip of the shaft portion 2. (preceding excavation step). The excavation holes 10 of the pair of enlarged bottom pile portions 1 are connected to the central axis O1 of the shaft portion 2 of each of the enlarged bottom pile portions 1 and the excavation holes 10 of the adjacent pair of enlarged bottom pile portions 1 in a later process. The ground G between the excavation holes 10 is excavated so that the central axis O2 of the excavation hole 11 of the connection pile portion 8 and the center axis O2 of the excavation hole 11 are mutually arranged on a straight line S1 in plan view.

On the other hand, in the cast-in-place concrete pile construction method of the present embodiment, before excavating and forming the excavation hole 10 of the shaft portion 2 of the expanded bottom pile portion 1, the shaft portion 2 of the adjacent expanded bottom pile portion 1 on the straight line S1 The ground G at the intermediate position is ground improved to form a ground improvement body 15 extending vertically in parallel with the shaft portion 2 of the enlarged bottom pile portion 1 (ground improvement step). This soil improvement body 15 is, for example, a columnar body such as soil cement, and has a compressive strength (uniaxial compressive strength, etc. ) is formed to increase the

The strength of the soil improvement body 15 may be set so that the ground G of the connecting pile portion 8 in the subsequent process can be excavated by the excavator 9 for piles, and is appropriately set according to the geological characteristics of the ground G. do it. That is, the strength characteristics of the soil improvement body 15 do not necessarily have to be limited as in the present embodiment.

Next, as shown in FIG. 1(d), a stabilizer 16, which is a positioning/guide projection that protrudes downward from the excavation blade coaxially with the central axis O3, is attached to the tip of the conventional pile excavator 9. Provided, the stabilizer 16 is abutted and pierced into the ground improvement body 15, and the ground G between the excavation holes 10 of the adjacent enlarged bottom pile portions 1 is subsequently excavated using the pile excavator 9 (following excavation process).

At this time, since excavation is performed by piercing the soil improvement body 15 with the stabilizer 16, the stabilizer 16 is guided by the soil improvement body 15 and guided in the vertical direction. As a result, even when the ground G between the excavation holes 10 of the adjacent enlarged bottom pile portions 1 is excavated using the pile excavator 9, bending does not occur, and the adjacent enlarged bottom pile portions 1 do not bend. The ground G between them can be preferably excavated (central excavation), and the excavated holes 10 of the adjacent enlarged bottom pile portions 1 can be connected with the excavated holes 11 of the connecting pile portions 8 .

Then, in this embodiment, after connecting the excavation holes 10 of the adjacent enlarged bottom pile portions 1 with the excavated holes 11 of the connecting pile portions 8, as shown in FIGS. The tip portions of the excavation holes 10 and 11 of the portion 1 and the connecting pile portion 8 are expanded using an excavator for expanding the bottom.

Here, as shown in FIG. 3, a plurality of soil improvement bodies 15 may be arranged side by side on another straight line S2 perpendicular to the straight line S1 in plan view. In addition, it is preferable that the plurality of soil improvement bodies 15 arranged on the other straight line S2 are formed such that adjacent soil improvement bodies 15 are partially overlapped with each other. By providing a plurality of soil improvement bodies 15 in this way, even when the interval between adjacent enlarged bottom pile portions 1 is narrowed, the soil improvement bodies 15 are less likely to break, and the ground is more reliably improved. By guiding the stabilizer 16 with the improved body 15, it becomes possible to excavate the center of the ground G between the excavation holes 10 of the adjacent enlarged bottom pile portions 1 suitably.

Furthermore, as shown in FIG. 4, after forming the soil improvement body 15, a guide hole 17 extending in the vertical direction is drilled in the center of the soil improvement body 15 using a boring machine or the like. The stabilizer 16 may be fitted/engaged to provide center drilling. Even in this case, since the stabilizer 16 can be guided in the vertical direction by the guide hole 17, even when narrowing the interval between the adjacent expanded bottom pile portions 1, the ground improvement body 15 is prevented from being bent or misaligned. Furthermore, it becomes possible to excavate the center more reliably and favorably.

Then, the excavation hole 10 of the adjacent enlarged bottom pile portion 1 composed of the shaft portion 2 and the enlarged bottom portion 3 and the excavated hole 11 of the connecting pile portion 8 composed of the shaft portion 2 and the enlarged bottom portion 3 are formed in communication. A reinforcing bar cage is erected in the connected excavation hole filled with , and concrete is placed using a tremie pipe so as to replace the stabilizing liquid (concrete placing process). If necessary, the pile head side is backfilled or a pile head foundation is constructed to complete the construction of the cast-in-place concrete pile 1'.

As shown in FIG. 5, the cast-in-place concrete pile 1' of the present embodiment constructed in this manner includes three expanded-bottom piles 1 and 8 each having a shaft portion 2 and an expanded-bottom portion 3. The central axes O1 and O2 of the shaft portions 2 of the piles 1 and 8 are arranged on the same straight line S1 in a plan view, and the shaft portions 2 and the expanded bottom portions 3 of the adjacent expanded bottom piles 1 and 8 are partially overlapped. It is built in an integrated form.

In other words, in the cast-in-place concrete pile 1' of the present embodiment, one surface 18a and the other surface 18b of the side surface of the shaft connection portion 18 in which the substantially cylindrical shaft portions 2 of the three expanded bottom piles 1 and 8 are integrated are It extends from the upper end to the lower end of the shaft connecting portion 18 and is formed so as to exhibit an arc uneven shape in which three convex arc surfaces 19 having a substantially constant diameter are connected in parallel. One surface 20a and the other surface 20b of the side surface of the enlarged bottom connecting portion 20 integrated with the enlarged bottom portion 3 have a conical concavo-convex shape in which three conical surfaces that gradually increase in diameter from the upper end to the lower end of the expanded bottom connecting portion 20 are connected in parallel. is formed to present

The cast-in-place concrete pile 1' of the present embodiment formed in this way can realize a pile with a high supporting strength by providing a large base area. In addition, in addition to the fact that the one surface 20a and the other surface 20b of the side surface of the expanded bottom connecting portion 20 are formed in a conical concavo-convex shape, the one surface 18a and the other surface 18b of the shaft connecting portion 18 are formed in a circular arc-concave shape. , the frictional resistance of the pile 1' can be greatly improved, and from this point, it is possible to realize the pile 1' with even higher supporting strength.

The bottom area of each of the enlarged bottom piles 1 and 8, and the total bottom area of the pile 1' consisting of the shaft connecting portion 18 and the enlarged bottom connecting portion 20, may be determined according to the required bearing capacity of the pile 1'.

Therefore, in the construction method of the cast-in-place concrete pile of the present embodiment, even if the pillars 5 of the building body 4 are close to each other in terms of design, the cast-in-place concrete pile 1' that provides necessary bearing capacity can be constructed. In addition, excavation of the adjacent enlarged bottom pile portion 1 and excavation of the connecting pile portion 8 can be performed using the same pile excavator 9 such as an R drill without bending the excavation hole 10 .

Therefore, according to the construction method of the cast-in-place concrete pile of this embodiment, compared with the conventional method, the cast-in-place concrete pile 1' having a high supporting strength that can suitably support a very large axial force of a column such as a skyscraper can be efficiently constructed. can be constructed economically and economically.

Although the first embodiment of the cast-in-place concrete pile construction method and the cast-in-place concrete pile according to the present invention has been described above, the present invention is not limited to the above-described first embodiment, and does not depart from the gist thereof. It can be changed as appropriate within the range.

For example, the cast-in-place concrete pile construction method (and cast-in-place concrete pile) of the present invention can be applied to the construction of a cast-in-place concrete pile 1 ′ having three or more expanded bottom pile portions 1 and two or more connecting pile portions 8. Of course, in this case as well, it is possible to obtain the same effects as those described in the present embodiment.

Further, the connecting pile portion 8 does not necessarily have to have an enlarged bottom pile shape including the shaft portion 2 and the enlarged bottom portion 3 . In other words, the shaft portion 2 alone may be formed and configured as long as a desired support strength can be obtained.

Next, a method for constructing a cast-in-place concrete pile (and a cast-in-place concrete pile) according to a second embodiment of the present invention will be described with reference to FIGS. In addition, in this embodiment, the same code|symbol is attached|subjected to the structure similar to 1st Embodiment, and the detailed description is abbreviate|omitted.

Here, in the first embodiment, the soil improvement body 15 is provided on the connecting pile portion 8, and after forming the excavation hole 10 of the shaft portion 2 of the adjacent expanded bottom pile portion 1, the stabilizer 16 is guided by the soil improvement body 15. to guide the excavator 9 in the vertical direction, and the excavation holes 10 of the adjacent enlarged bottom pile portions 1 are connected by the excavation holes 11 of the enlarged bottom piles serving as the connecting pile portions 8 .

In this case, since the excavation holes 10 of the large expanded pile portion 1 are formed in advance on both sides of the ground G of the connecting pile portion 8 and thus the ground improvement body 15, the geological properties of the ground G (a fragile gravel layer etc.), it is conceivable that the ground G may collapse or the ground improvement body 15 may break during central excavation for excavating the ground G of the connection pile portion 8 .

On the other hand, in the construction method of the cast-in-place concrete pile of this embodiment, as shown in FIGS. , the ground G of each enlarged bottom pile portion 1 is ground improved to form a soil improvement body 15 on the central axis O1 of each enlarged bottom pile portion 1 (soil improvement step).

Then, before forming the excavated holes 10 of the enlarged bottom pile portions 1, the excavated holes 11 of the connecting pile portions 8 are excavated using the excavator 9 for piles (preceding excavation step).

Next, as shown in FIGS. 6(a) to 6(d), 7(a), and 7(b), the stabilizer 16 is pierced into the soil improvement body 15 provided on the expanded bottom pile portion 1, While guided and guided by the soil improvement body 15, the excavation hole 10 of one of the adjacent enlarged bottom pile portions 1 and the excavation hole 10 of the other adjacent enlarged bottom pile portion 1 are excavated and formed by the pile excavator 9 (following excavation step ).

Further, as shown in FIGS. 8(a) to 8(d), the expanded bottom portion 3 of the connecting pile portion 8 and the expanded bottom portions 3 of the pair of expanded bottom pile portions 1 are excavated using a bottom expanding excavator. Here, as shown in FIG. 8A, it is preferable that the enlarged bottom diameter of the connecting pile portion 8 is equal to or larger than the length at which the enlarged bottom portions 3 of the pair of enlarged bottom pile portions 1 intersect. By setting the expanded bottom diameter of the connecting pile portion 8 in this way, it is possible to more reliably prevent the ground between the piles from collapsing.

As a result, as in the first embodiment, one excavation hole 10 of the adjacent enlarged bottom pile portion composed of the shaft portion 2 and the enlarged bottom portion 3 and an excavated hole 11 of the connecting pile portion 8 composed of the shaft portion 2 and the enlarged bottom portion 3 are formed. Connected drilled holes are formed, and reinforcing bar cages are erected in these linked drilled holes filled with a stabilizing liquid, and concrete is placed using a tremie pipe (concrete placing step), in the same manner as in the first embodiment. of cast-in-place concrete piles 1' can be constructed.

In this way, a ground improvement body 15 is provided on a pair of adjacent expanded bottom pile portions 1, and after excavating the excavation hole 11 of the connecting pile portion 8, the excavating hole 10 of the expanded bottom pile portion 1 is excavated to form a connecting excavation hole. Therefore, in the construction method of the cast-in-place concrete pile of the present embodiment, in a state in which there are no excavation holes on both outer sides (a state in which there is no excavation hole on at least one of the outer sides), the excavation holes 11 of the connecting pile portion 8, the enlarged bottom pile portion One borehole 10 can be formed.

In addition, a ground improvement body 15 is provided on the expanded bottom pile portion 1, and after forming the excavation hole 11 of the connecting pile portion 8, the excavator 9 is positioned vertically by the ground improvement body 15 and the stabilizer 16, and while guiding/guiding each bottom expansion. By forming the excavation hole 10 of the pile portion 1 to form a connected excavation hole, it is possible to prevent bending, ground, and breakage of the ground improvement body 15 from occurring more reliably than the first embodiment during excavation. The cast-in-place concrete pile 1' made up of the connecting drilled hole, and thus the shaft connecting portion 18 and the expanded bottom connecting portion 20 can be suitably formed and constructed.

Therefore, in the construction method of the cast-in-place concrete pile of this embodiment, it is possible to construct the cast-in-place concrete pile 1 ′ that provides the necessary bearing force more reliably than in the first embodiment, and the adjacent expanded bottom pile portion 1 Excavation and excavation of the connecting pile portion 8 can be performed using the same pile excavator 9 such as an R drill without bending the excavation holes 10 and 11 .

Therefore, according to the construction method of the cast-in-place concrete pile of the present embodiment, compared with the conventional method and further compared with the first embodiment, a high support strength that can suitably support a very large column axial force such as a skyscraper of cast-in-place concrete piles 1' can be constructed efficiently and economically.

Although the second embodiment of the cast-in-place concrete pile construction method (and the cast-in-place concrete pile) according to the present invention has been described above, the present invention is not limited to the above-described second embodiment, and the first embodiment. It can be changed as appropriate without departing from the gist of the invention, including modifications of the form.

1 Cast-in-place concrete pile (expansion pile part, expansion pile)
1' Cast-in-place concrete pile 1a Pile bottom 2 Shaft 3 Enlarged bottom 4 Building body 5 Column 7 Foundation 8 Connecting pile 9 Excavator 10 Excavating hole of expanding pile 11 Excavating hole of connecting pile 14 Wall 15 Soil improvement body 16 Stabilizer (positioning/guide protrusion)
17 Guide hole 18 Shaft connection portion 18a One surface 18b Other surface 19 Convex arc surface 20 Enlarged bottom connection portion 20a One surface 20b Other surface G Ground O1 Central axis O2 Central axis O3 Central axis P Load S1 Straight line S2 Other straight line

Claims (6)

A connection that connects an enlarged bottom pile portion composed of a cylindrical shaft portion and an enlarged bottom portion in a substantially truncated cone shape formed by expanding the tip of the shaft portion, and the adjacent enlarged bottom pile portions provided at a predetermined interval. A method of constructing a cast-in-place concrete pile comprising:
A ground improvement step of forming a columnar ground improvement body by improving the ground of a pair of adjacent enlarged bottom pile parts or the ground of the connecting pile part,
A preceding excavation step of pre-excavating the ground of the connecting pile portion that does not form the ground improvement body or the ground of the pair of adjacent enlarged bottom pile portions using an excavator for piles to form an excavation hole;
Subsequent excavation is performed while using an excavator for piles and guiding in the vertical direction by the ground improvement body, the ground of the adjacent pair of enlarged bottom pile parts forming the ground improvement body, or the ground of the connecting pile part. a succeeding excavation step of forming a cylindrical excavation hole and communicating with the excavation hole formed by the preceding excavation to form a connected excavation hole;
A method of constructing a cast-in-place concrete pile, characterized by comprising a concrete placing step of placing concrete in the connected excavated holes formed by the excavated holes of the adjacent enlarged bottom pile portions and the excavated holes of the connected pile portions. In the construction method of the cast-in-place concrete pile according to claim 1,
In the trailing excavation step, a stabilizer is provided at the tip of the excavator for piles and is a positioning/guide projection projecting downward from the excavation blade coaxially with the central axis of the excavator for piles,
A method for constructing a cast-in-place concrete pile, characterized in that the stabilizer is pierced into the soil improvement body and trailing excavation is performed while guiding the excavator for the pile in the vertical direction with the soil improvement body and the stabilizer. In the construction method of the cast-in-place concrete pile according to claim 1 or claim 2,
A method for constructing a cast-in-place concrete pile, wherein in the ground improvement step, the ground improvement body is formed so that the compressive strength is increased by the ground improvement. In the construction method of the cast-in-place concrete pile according to any one of claims 1 to 3,
In the ground improvement step, a plurality of the ground improvement bodies are arranged side by side on another straight line perpendicular to the straight line connecting the central axis of the pair of adjacent enlarged bottom pile parts and the central axis of the connecting pile part in plan view. A method for constructing a cast-in-place concrete pile characterized by: In the construction method of the cast-in-place concrete pile according to claim 2,
In the ground improvement step, a ground improvement body is formed by improving the ground on the central axis of the pair of adjacent enlarged bottom pile parts or the ground on the central axis of the connecting pile part,
drilling the soil improvement body on the central axis to form a guide hole extending in the vertical direction in the soil improvement body;
In the trailing excavation step, the trailing excavation is performed while the stabilizer is engaged with the guide hole to guide the excavator for the pile in the vertical direction. An enlarged bottom pile portion consisting of a cylindrical shaft portion and an enlarged bottom portion in a substantially truncated cone shape formed by expanding the tip of the shaft portion, and a circle connecting the adjacent enlarged bottom pile portions provided at a predetermined interval. In a cast-in-place concrete pile having a columnar connecting pile portion,
At least three convex arcs extending from the top end to the bottom end of the shaft connecting portion on one side surface and the other side surface of the shaft connecting portion integrally connecting the shaft portions and the connecting pile portions of the pair of adjacent enlarged bottom pile portions. A cast-in-place concrete pile characterized by being formed so as to exhibit an arcuate concavo-convex shape in which faces are arranged in parallel.

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