JP7301185B2 - cast-in-place concrete pile - Google Patents

Description

The present invention relates to cast-in-place concrete piles.

Conventionally, cast-in-place concrete expanded bottom piles are often used as pile foundations for heavy buildings such as skyscrapers. In such a cast-in-place concrete expanded bottom pile (hereinafter referred to as a cast-in-place concrete pile), for example, as shown in Patent Document 1, a shaft portion having a substantially constant diameter and a tip end side of the shaft portion having a necessary bearing force There is known a structure that is constructed with a substantially truncated cone-shaped enlarged bottom portion that is enlarged in accordance with the tip of the pile, and that greatly improves the bearing strength by providing the enlarged bottom portion at the tip of the pile.

When constructing a cast-in-place concrete 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 filling it with a stabilizing liquid. Next, at the stage where the bottom enlarging excavator 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 bottom enlarging excavator to extract the ground of the hole wall portion. is excavated and the tip of the excavated hole is widened. 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.

Here, as shown in FIG. 8(a), the size of the cast-in-place concrete pile 1A constructed as described above differs for each construction method. is about 3 m at the maximum, and the expanded bottom diameter (the outer diameter of the expanded bottom portion 20A) is 4.8 m to 5.5 m at the maximum.
On the other hand, in the cast-in-place concrete pile 1B, which receives a very large axial force of a column such as a skyscraper, the bearing capacity may be insufficient even with the maximum expanded bottom diameter. As shown, countermeasure construction methods such as forming a plurality of expanded bottom portions 20B in the vertical direction of the shaft portion 10 have been proposed and put into practical use.

Furthermore, as in the cast-in-place concrete pile 1C shown in FIG. 8(c), in order to increase the bearing capacity of the pile, the bottom expansion excavation length is increased to form an expanded bottom portion 20C that is excavated into a beer bottle shape. However, a method of increasing the peripheral friction of piles has also been implemented (see, for example, Non-Patent Document 1).

Japanese Patent No. 2607966

Yasuaki Hirakawa, Junji Hamada, Kiyoshi Yamashita, "Foundation Structural Design and Construction of Abeno Harukas," Foundation Engineering, 2014.11, p. 029-036

However, in conventional cast-in-place concrete piles in which two or more enlarged bottom portions are separated, it is necessary to excavate a hard support layer to increase the length of the pile by the amount of the increased enlarged bottom portion, which affects construction costs and processes. Very large impact. For this reason, there is a strong demand for a technique that enables more efficient and effective improvement of supporting strength.

In addition, in order to increase the bearing capacity of the pile, the expanded bottom excavation length as shown in FIG. In this case, the tip bearing force that can ensure a large bearing force remains the same as before, and only the peripheral frictional force increases. Therefore, there is a problem that the excavation amount of the support layer G2 increases.
Furthermore, in this case, the amount of excavated soil and the amount of placed concrete are proportional to the square of the excavation diameter, but since the peripheral area is proportional to the excavation diameter, the cost to secure the bearing capacity increases. There was room for improvement in that respect.

The present invention has been made in view of the above-mentioned problems, and can improve the support strength more efficiently and effectively than the conventional art, and can reduce the construction cost and construction time. It is intended to provide cast-in-place concrete piles.

In order to achieve the above object, a cast-in-place concrete pile according to the present invention has a cylindrical shaft and an enlarged bottom portion formed by expanding the tip of the shaft using a bottom-enlarging excavator. In the concrete pile, the expanded bottom portion has an upper expanded bottom portion and at least one lower expanded bottom portion in the vertical expanded bottom portion extending downward from the upper expanded bottom portion, and the upper expanded bottom portion is viewed in plan cross section. It is constructed in a shape having a circular portion centered on the central axis of the shaft portion, and the lower expanded bottom portion protrudes radially outward from a circular outer surface centered on the central axis of the shaft portion in plan cross-sectional view, Constructed with a convex arc portion that is not concentric with the circular portion of the upper expanded bottom portion , and the convex arc portion of the lower expanded bottom portion is radially outward of the circular portion of the upper expanded bottom portion. The bottom enlarging excavator includes a rod rotatably supported by a rotation support device placed on the ground, an excavator body provided at the lower end of the rod, and a diameter from the outer peripheral surface of the excavator body. and a stabilizer projecting downward coaxially with the rod axis from the center of the tip of the excavator body. , the length in the axial direction of the rod from the upper end of the excavator main body to the tip of the stabilizer, and the vertical excavation length of the expanded bottom portion in the vertical direction is equal to or greater than the total height of the excavator for expanding the bottom. there is

In the present invention, by moving the bottom-enlarging excavator to the eccentric position, it is possible to easily construct the lower-enlarged-bottom portion that is larger than the upper-enlarged-bottom portion. That is, in the cast-in-place concrete pile of the present invention, the lower expanded bottom portion (pile bottom surface) has a convex arc portion that protrudes radially outward from the circular outer surface of the vertically expanded bottom portion centered on the central axis of the vertically expanded bottom portion in a plan view. It is possible to construct a bottom-enlarged pile having a bottom area of the bottom surface of the pile in the bottom-enlarged bottom portion that is about twice or more as large as the maximum bottom-enlargement diameter of the excavator for bottom-enlargement.
Thus, in the present invention, since the base area of the pile is large, the cast-in-place concrete pile can bear a large bearing capacity. Therefore, there is no need to excavate the whole support layer for bottom expansion or to deeply excavate the support layer in order to provide a plurality of expanded diameter portions, as in the case of providing a conventional beer bottle-shaped expanded bottom portion. An increase in the amount can be suppressed, and a reduction in construction cost and construction time can be achieved.

According to the cast-in-place concrete pile of the present invention, it is possible to improve the supporting strength more efficiently and effectively, and to reduce the construction cost and construction time, as compared with conventional piles.

It is a side view which shows the structure of the excavation hole of the cast-in-place concrete pile by embodiment of this invention. (a) and (b) are a side view showing a case where an enlarged bottom portion is formed using a conventional enlarged bottom excavator, and a plan view showing the outer diameter of each excavated portion. It is a side view showing the construction method of the cast-in-place concrete pile, (a) is a diagram showing the shaft portion, and (b) is a diagram showing a state in which bottom expansion excavation is being performed for the upper expanded bottom portion and the vertical expanded bottom portion. (a) and (b) are side views showing a method of constructing a cast-in-place concrete pile, showing a state in which the bottom enlarging excavator is placed at an eccentric position. (a) and (b) are side views showing a method of constructing a cast-in-place concrete pile, showing a state in which bottom expansion excavation is being performed on a bottom expansion portion by a bottom expansion excavator. It is a plan view showing a method of constructing a cast-in-place concrete pile, (a) is a diagram when bottom expansion excavation is performed at four eccentric positions, and (b) is a case where bottom expansion excavation is performed at six eccentric positions. , and (c) is a diagram when bottom expansion excavation is performed at eight eccentric positions. (a), (b), and (c) are simplified views of FIGS. 6(a), (b), and (c), respectively. (a), (b), and (c) are diagrams showing a conventional cast-in-place concrete pile.

Hereinafter, a cast-in-place concrete pile according to an embodiment of the present invention will be described based on the drawings.

In the construction method of the cast-in-place concrete pile 1 of the present embodiment, as shown in FIG. ) and a method for constructing The cast-in-place concrete pile 1 has a support layer G2 positioned below the normal ground (soft layer G1 in this case), and a tip portion 10a of the shaft portion 10, i. part of the enlarged bottom 23) is arranged.

The expanded bottom portion 2 (21, 22, 23) is formed using a well-known excavator 3 for expanding the bottom, as shown in FIGS. The bottom enlarging excavator 3 is formed by excavating the excavating hole 2A of the enlarging bottom portion 2 in the shaft portion 10 (the large diameter shaft 11 and the small diameter shaft 12) having a diameter in the range of φ2.1 to 3.0 m, for example. available equipment is adopted. Here, FIGS. 2(a) and 2(b) show a method of constructing a conventional cast-in-place concrete pile in which only one expanded bottom portion 2 is provided at the tip of the shaft portion 10. As shown in FIG.

In the construction method of the cast-in-place concrete pile 1, first, as shown in FIG. Excavation is performed while filling the stabilizing liquid to a depth to form the first excavation hole 10A of the shaft portion 10 of the cast-in-place concrete pile 1 having a substantially constant shaft diameter (for example, 3.0 m).

Next, as shown in FIG. 3B, for example, a bottom-enlarging excavator 3 (first bottom-enlarging excavator, second bottom-enlarging excavator) having a maximum bottom-enlarging diameter of 4.0 m or more is used. The excavator 3 is inserted into the tip portion of the first excavation hole 10A of the shaft portion 10, and the center axis (rod axis C1) of the bottom enlarging excavator 3 is aligned with the center axis O of the shaft portion 10. (the position of the two-dot chain line of symbol P1 in FIG. 3(b)).

As shown in FIG. 3B, the bottom enlarging excavator 3 includes a rod 31 rotatably supported by a rotation support device (not shown) placed on the ground, and a tip (lower end) of the rod 31. a cylindrical excavator body 32, a pair of left and right expansion wings 33 provided so as to protrude from an outer peripheral surface 32a of the excavator body 32 in a radial direction orthogonal to the rod axis C1 of the rod 31, and an excavator body. A stabilizer 34 (positioning protrusion) protruding downward coaxially with the rod axis C1 from the center of the bottom surface 32b (tip) of the stabilizer 32 is provided.

The rod 31 is rotatably supported about the rod axis C1 with the direction of the rod axis C1 directed vertically, and the lower end of the rod is integrally fixed to the center of the upper surface of the excavator main body 32 . The excavator main body 32 is rotated around the rod axis C1 as the rod 31 is rotated.

The expansion wing 33 has a generally triangular plate shape that extends radially outward from top to bottom when viewed from the side, and has a plurality of excavating blades (illustrated omitted) is provided. The outer diameter of the expansion wing 33 when it protrudes most from the excavator main body 32 is the maximum bottom expansion diameter of the excavator 3 for expanding the bottom. A pair of expansion wings 33 are provided at positions facing each other on both sides of the excavator main body 32 when viewed from the direction of the rod axis C1.

As shown in FIG. 4(a), the stabilizer 34 constitutes a positioning projection for stabilizing the bottom enlarging excavator 3 by hitting and piercing the bottom surface of each excavation hole. In addition, the stabilizer 34 of the present embodiment is formed in a tapered and pointed shape at the tip portion in the projecting direction. It may also be shaped like a drill or an auger so that it can easily penetrate into the ground below.

Next, as shown in FIG. 3(b), the hole wall of the tip portion 10a (see FIG. 3(a)) of the first excavation hole 10A of the shaft portion 10 formed by pre-excavation is removed by the bottom enlarging excavator 3. The expanded bottom portion 2 is coaxial with the first dug hole 10A of the shaft portion 10 by digging so as to expand while expanding the expansion wings 33, that is, extends downward from the second dug hole 21A of the upper expanded bottom portion 21 and the upper expanded bottom portion 21. 22 A of 3rd excavation holes of the vertically expanded bottom part 22 are formed. The upper enlarged bottom portion 21 is formed in a shape having a circular portion centered on the central axis of the shaft portion 10 in plan cross-sectional view.

As a specific construction method, the excavator main body 32 connected to the lower end of the rod 31 is inserted and arranged up to the tip of the first excavation hole 10A of the shaft portion 10 (second symbol P1 shown in FIG. 3B). position of the dash-dotted line). At this time, the stabilizer 34 of the bottom enlarging excavator 3 is pierced into the ground of the bottom surface of the pile of the first excavation hole 10A of the shaft portion 10, and the excavator main body 32 is positioned so as not to shift in the left-right direction for better stability. It is preferable to increase

Subsequently, the bottom enlarging excavator 3 is expanded and rotated around the rod axis C1 to excavate the hole wall portion of the first excavating hole 10A of the shaft portion 10 to expand the bottom of the first excavating hole 10A of the shaft portion 10. An excavation hole of a substantially truncated cone-shaped expanded bottom portion 2 is formed in the tip portion. Here, the expansion wings 33 of the excavator 3 for bottom expansion are expanded in the maximum expanded state, and the amount of expansion may be set according to the diameter dimension of the expanded bottom portion 2 set at this time.

After the substantially truncated conical expanded bottom portion 2 is formed at the tip of the first excavation hole 10A of the shaft portion 10, the bottom expanding excavator 3 is rotated to move the excavator main body 32 together with the rod 31 to a predetermined depth position. By excavating while pulling up to (here, the position of the upper expanded bottom portion 21), the expanded bottom portion 2 in the shape of a beer bottle is formed. That is, since the inclined portion 33a having the excavating blade in the expansion wing 33 is arranged upward, the excavator main body 32 is pulled up to excavate the first excavating hole 10A of the shaft portion 10 to expand the diameter of the shaft portion 10. A vertically enlarged bottom portion 22 is formed which is coaxial with the central axis O and has a maximum enlarged bottom diameter when the expansion wings 33 are projected. At a predetermined position where the excavator main body 32 is stopped from being pulled up (the position indicated by the solid line P3 in FIG. 3(b)), the upper enlarged bottom portion 21 is formed.
In FIG. 3(b), the excavator 3 for bottom expansion located at the position indicated by the chain double-dashed line P2 is in the process of being pulled up from the position P1 to the position P3.

The excavation length L1 (the height from the bottom surface of the shaft portion 10) of the third excavation hole of the vertically enlarging bottom portion 22 is determined by the excavator main body 32 and the stabilizer 34 of the excavator 3 for bottom enlarging, as shown in FIG. The length (total height) in the direction of the rod axis C1 to the tip of the rod is set to be equal to or greater than Lm.

As shown in FIGS. 4(a) and 4(b), the outer diameter of the lower end of the second excavated hole 21A of the upper expanded bottom portion 21 and the outer diameter of the third excavated hole 22A of the vertically expanded bottom portion 22 are determined by the excavator When the main body 32 is arranged in the vertically expanded bottom portion 22, the position where the rod 31 contacts the hole wall of the shaft portion 10 and the outer peripheral surface 32a of the excavator main body 32 with the expansion wings 33 closed are the vertically expanded bottom portion. It is determined by at least one (both in this embodiment) of the positions of contact with the hole wall of the third excavation hole 22A of 22 .

Next, as shown in FIGS. 4(a) and 4(b), the bottom enlarging excavator 3 is positioned at a predetermined depth of the third excavation hole 22A of the vertically enlarging bottom portion 22 (position near the hole bottom, FIG. 4(a)). )), and slide the rod axis C1 of the bottom enlarging excavator 3 in the horizontal direction with respect to the central axis O of the shaft portion 10 by a predetermined eccentricity N to make it eccentric. placed. The eccentric position (position Q2 in FIG. 4A and position Q3 in FIG. 4B) of the bottom enlarging excavator 3 in this embodiment is such that the rod 31 contacts the hole wall of the shaft portion 10. position, and the outer peripheral surface 32a of the excavator main body 32 with the expansion wings 33 closed contacts the hole wall of the third excavation hole 22A of the vertically expanded bottom portion 22 . At this time, as shown in FIG. 4(b), the stabilizer 34 of the bottom enlarging excavator 3 is pierced into the ground of the bottom surface of the third excavation hole 22A of the vertically enlarging bottom portion 22 so that the excavator main body 32 is not displaced in the left-right direction. position (state of symbol Q3).

In this embodiment, when the bottom-enlarging excavator 3 is eccentrically moved, positioning and holding means (not shown) such as an eccentric bottom-enlarging excavating guide for guiding the rod 31 to a predetermined eccentric position may be used.
In this case, when the bottom-enlarging excavator 3 is rotated around the rod axis C1 to excavate the hole wall, the bottom-expanding excavator 3 is held at its eccentric position by the positioning and holding means, and the bottom-expanding excavation can be preferably performed. .

Next, as shown in FIG. 5(a), from the excavator main body 32 arranged at a position eccentric to the hole wall of the third excavation hole 22A of the vertically expanded bottom portion 22, the expansion wings 33 are spread around the rod axis C1. The fourth excavation hole 23A of the lower enlarged bottom portion 23 is formed by rotating and expanding the bottom enlarged excavation (see FIGS. 6A, 6B, and 6C). At this time, the expansion wings 33 of the excavator 3 for bottom expansion are expanded in a state of being expanded to the maximum. be. The lower enlarged bottom portion 23 is constructed to have a convex arc portion 23a protruding radially outward from the vertical enlarged bottom portion 22 in a cross-sectional plan view. The convex arc portion 23 a of the lower enlarged bottom portion 23 is positioned radially outside the circular portion of the upper enlarged bottom portion 21 .

Next, as shown in FIG. 5(b), the bottom enlarging excavator 3 is horizontally slid from the position Q3 shown in FIG. 4(a) to be placed at another eccentric position (position Q4). . Then, after fixing the stabilizer 34 of the excavator 3 for bottom expansion to the ground of the bottom surface of the third excavation hole 22A of the vertical expansion bottom part 22 as described above, the expansion wing 33 is expanded to perform bottom expansion excavation, and the position of the code Q4 is obtained. 23A of the fourth excavated holes of the lower enlarged bottom portion 23 are formed.

By performing such bottom-enlarging excavation several times at a plurality of eccentric positions, a cast-in-place excavator exceeding the maximum bottom-enlarging diameter of the excavator 3 for bottom-enlarging as shown in FIGS. A concrete pile 1 can be constructed. FIGS. 7(a), (b), and (c) are diagrams showing only the bottom enlarging excavator 3 at two eccentric positions in FIGS. 6(a), (b), and (c), respectively. FIG. 6(a) shows a state in which the fourth excavated holes 23A of the lower expanded bottom portion 23 are formed at four locations around the shaft portion 10 at regular intervals. That is, in FIG. 6(a), bottom enlarging excavation was performed four times by arranging the excavator 3 for bottom enlarging at each of four eccentric positions. FIG. 6(b) is obtained by arranging the bottom enlarging excavator 3 at each of six eccentric positions and performing bottom enlarging excavation six times. FIG. 6(c) is obtained by arranging the bottom enlarging excavator 3 at each of eight eccentric positions and performing bottom enlarging excavation eight times.
The cast-in-place concrete pile 1 of the present embodiment constructed in this manner has a circular outer surface of the vertically expanded bottom portion 22 centered on the central axis O of the shaft portion 10 (the third excavation hole 22A). It is constructed with a convex arc projecting radially outward from the bore wall).

Next, as shown in FIG. 1, each of the drilled holes 10A, 21A, 22A, and 23A of the shaft portion 10, the upper enlarged bottom portion 21, the vertical enlarged bottom portion 22, and the lower enlarged bottom portion 23 is replaced with a stabilizing liquid using a tremie tube. A cast-in-place concrete pile 1 is constructed by pouring concrete so as to do. In addition, inserting a reinforcing bar cage into each excavation hole 10A, 21A, 22A, 23A, backfilling the pile head side as necessary, constructing a pile head foundation, etc., Construction is completed.

Next, the operation of the cast-in-place concrete pile 1 will be described in detail based on the drawings.
According to the construction method of the cast-in-place concrete pile 1 of the present embodiment, as shown in FIGS. By performing the work of moving to the position, the lower enlarged bottom portion 23 enlarged larger than the upper enlarged bottom portion 21 can be easily constructed. That is, in the cast-in-place concrete pile 1 of this embodiment, the pile bottom surface of the lower expanded bottom portion 23 protrudes radially outward from the circular outer surface of the vertically expanded bottom portion 22 centered on the central axis O of the vertically expanded bottom portion 22 in a plan cross-sectional view. The bottom area of the pile bottom surface 23b in the lower enlarged bottom portion 23 is about twice or more than the maximum enlarged bottom diameter of the excavator 3 for bottom enlargement. It is possible to construct a large expanded bottom pile.

Thus, in this embodiment, since the base area of the pile is large, the cast-in-place concrete pile 1 can bear a large bearing force. Since it is not necessary to excavate the entire support layer for bottom expansion or to provide a plurality of expanded diameter portions, it is not necessary to excavate the support layer G2. can be suppressed, and the construction cost and construction time can be reduced.

In addition, in the present embodiment, since the excavation length L1 in the vertical direction in the third excavation hole 22A of the vertically expanded bottom portion 22 is equal to or greater than the total height Lm of the bottom expanding excavator 3, the vertically expanded bottom portion 22 is not further excavated. The bottom enlarging excavator 3 can be slid horizontally and eccentrically within the third excavation hole 22A of the vertical bottom enlarging portion 22, thereby improving work efficiency for construction work.

Further, in the present embodiment, even if the bottom surface of the previously excavated excavated hole is formed in a mortar shape, or even if the ground is easy to collapse such as sand and gravel, when excavating the expanded bottom portion 2 by subsequent excavation, the excavated hole The excavator 3 for bottom enlargement can be arranged so that the stabilizer 34 of the excavator 3 for bottom enlargement pierces the bottom surface at a position where the rod axis C1 is eccentric from the center axis of the bottom. Therefore, the bottom enlarging excavator 3 is stabilized, and in this state, the bottom enlarging excavator 3 can rotate around the rod axis C1 to excavate the wall of the excavation hole for bottom enlarging. That is, the excavator 3 for bottom enlargement arranged at an eccentric position can perform bottom enlargement excavation without misalignment, and the cast-in-place concrete pile 1 exceeding the maximum bottom enlargement diameter of the excavator 3 for bottom enlargement can be reliably and suitably constructed. be able to.

As described above, in the cast-in-place concrete pile according to the present embodiment, it is possible to improve the supporting strength more efficiently and effectively than the conventional pile, and it is possible to reduce the construction cost and construction time.

Although the embodiment of 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 embodiment, and can be appropriately modified within the scope of the invention.

For example, as in the present embodiment, the expanded bottom diameters of the second excavated hole 21A of the upper expanded bottom portion 21 and the fourth excavated hole 23A of the lower expanded bottom portion 23 are set to the maximum by widening the expansion wings 33 of the excavator 3 for bottom expansion. It is not limited to being formed with an enlarged bottom diameter. In other words, since it is sufficient to construct the expanded bottom portion with the required enlarged bottom area, the expanded wings 33 should be widened to have a diameter corresponding to the enlarged bottom area.

In addition, in the present embodiment, the bottom-enlarging excavator 3 for excavating the second excavating hole 21A of the upper-stage enlarging bottom portion 21 and the third excavating hole 22A of the vertical enlarging-bottom portion 22, and the fourth excavating hole 23A of the lower-stage enlarging bottom portion 23 are excavated. Although the same excavator is used as the bottom enlarging excavator 3, excavators having different configurations may be used. Also, the shape and configuration of the bottom enlarging excavator 3 are not limited to the above-described embodiment.

Furthermore, as a method for excavating the second excavation hole 21A of the upper expanded bottom portion 21 and the third excavated hole 22A of the vertical expanded bottom portion 22, the excavator main body 32 is arranged at the tip of the shaft portion 10, and the expansion wings 33 are spread upward. Although the method of excavating by pulling up is used, the method is not limited to the method of this embodiment, and other construction methods can be adopted. For example, it is also possible to adopt a construction method in which the upper expanded bottom portion 21 is constructed first, and then expanded bottom excavation is performed to the tip of the shaft portion 10 while rotating the expanded wing 33 of the excavator 3 for bottom expansion in a protruded state.

Further, for example, in advance, the entire ground directly under the pile bottom or the ground at the portion where the stabilizer 34 hits (the ground directly under the pile bottom at the eccentric position) may be ground improved using a deep ground improvement method or the like. In this case, when the bottom-enlarging portion is excavated by the trailing excavation, the bottom-enlarging excavator can be further stabilized to perform the bottom-enlarging excavation of the hole wall of the excavation hole, so that the bottom-enlarging excavation is more reliable and suitable. It is possible to construct a bottom expansion pile that exceeds the maximum bottom expansion diameter of the machine.

In addition, it is possible to appropriately replace the components in the above-described embodiments with well-known components without departing from the scope of the present invention.

1 cast-in-place concrete pile 2 bottom expansion part 3 bottom expansion excavator (first bottom expansion excavator, second bottom expansion excavator)
10 shaft portion 10A first drilling hole of shaft portion 21 upper enlarged bottom portion 21A second drilling hole 22 vertical enlarged bottom portion 22A third drilling hole 23 lower enlarged bottom portion 23A fourth drilling hole 23a convex arc portion 23b pile bottom surface 31 rod 32 excavator Main body 33 Extended wing 34 Stabilizer (positioning protrusion)
C1 rod axis (central axis of excavator for bottom expansion)
O Center of shaft G1 Weak layer G2 Support layer

Claims (1)

A cast-in-place concrete pile having a cylindrical shaft and an expanded bottom formed by expanding the tip of the shaft using a bottom-expanding excavator,
The expanded bottom portion has an upper expanded bottom portion and at least one lower expanded bottom portion in the vertical expanded bottom portion extending downward from the upper expanded bottom portion,
The upper enlarged bottom portion is constructed in a shape having a circular portion centered on the central axis of the shaft portion in plan view,
The lower enlarged bottom portion has a convex arc portion that protrudes radially outward from a circular outer surface centered on the central axis of the shaft portion in plan cross-sectional view and is not concentric with the circular portion of the upper enlarged bottom portion. built in the form of
the convex arc portion of the lower expanded bottom portion is positioned radially outside the circular portion of the upper expanded bottom portion;
The excavator for expanding the bottom includes a rod rotatably supported by a rotation support device arranged on the ground, an excavator main body provided at the lower end of the rod, and an excavator main body extending radially from the outer peripheral surface of the excavator main body. an expandable wing, and a stabilizer protruding downward coaxially with the rod axis from the center of the tip of the excavator body,
The total height of the bottom-enlarging excavator is the length in the axial direction of the rod from the upper end of the excavator body to the tip of the stabilizer,
A cast-in-place concrete pile characterized in that the excavation length in the vertical direction of the expanded bottom part in the vertical direction is equal to or greater than the total height of the excavator for expanding the bottom.

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