JP2019183497A - Cast-in-place concrete pile construction method and cast-in-place concrete pile - Google Patents

Abstract

To provide a cast-in-place concrete pile construction method capable of more efficiently and effectively improving the bearing strength than conventional ones, and a cast-in-place concrete pile.SOLUTION: The cast-in-place concrete pile construction method includes the steps of: forming an excavation hole 10 in a shaft 2 to a predetermined depth of the ground G using a bottom-excavating excavator 5 by performing pre-drilling; inserting the bottom-excavating excavator 5 for a shaft having a smaller diameter than the drilling hole 10 of the shaft 2 into the tip edge of the drilling hole 10 of the shaft 2; disposing the center axis O2 of the bottom-excavating excavator 5 being displaced by a predetermined amount with respect to the center axis O1 of the shaft part 2; and forming a drilling hole 11 in the bottom expansion part 3 by performing trailing drilling to expand the hole wall of the tip edge of the drilling hole 10 of the shaft 2 formed by the previous excavation with the bottom-excavating excavator 5.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, cast-in-place concrete bottom piles are often used as pile foundations in heavy buildings such as high-rise buildings.

  A cast-in-place concrete pile (cast-in-place concrete pile) has a shaft portion with a substantially constant diameter and a bottom portion in the shape of a truncated cone that is formed by expanding the tip of the shaft portion according to the required support force. The support strength can be significantly improved by providing an expanded bottom portion at the tip of the pile (see, for example, Patent Document 1).

  When constructing the cast-in-place concrete bottom pile, for example, an excavator is used to form an excavation hole having a substantially constant diameter from the ground surface while filling it with a stable liquid to a predetermined depth. Next, at the stage where a bottom-excavating machine (bottom-expanding machine such as a bottom-up bucket) connected to the tip of the rod is inserted and placed at the tip of the excavation hole, the rod is moved around the central axis while expanding the bottom-excavating excavator. Rotate to excavate the ground of the hole wall and widen the tip of the excavation hole. Then, reinforced rods are built into the expanded excavation hole, and concrete is laid to replace the stable liquid using a tremy pipe, and the pile head side is backfilled or a pile head foundation is constructed as necessary. The construction of cast-in-place concrete expanded piles is completed.

Japanese Patent No. 2607966

  Here, as shown in FIG. 6A, the cast-in-place concrete expanded bottom pile 1 constructed as described above has a different size for each method, but at present, the shaft diameter (diameter of the shaft portion 2). Is about 3 m at the maximum and the expanded diameter (the diameter of the expanded portion 3) is at most 4.8 m to 5.5 m.

  On the other hand, in piles that receive very large column axial force such as high-rise buildings, the support force may be insufficient even at the maximum bottom diameter. To compensate for the lack of support force, for example, as shown in FIG. A countermeasure method such as forming a plurality of the widened portions 3 has been proposed and put into practical use.

  However, when forming two or more bottom expanded parts 3, it is necessary to excavate the hard support layer G1 and lengthen the pile length, and the influence on construction cost and process is very large. For this reason, a technique that makes it possible to improve the bearing strength more efficiently and effectively is strongly desired.

  In view of the above circumstances, an object of the present invention is to provide a method for constructing a cast-in-place concrete pile and a cast-in-place concrete pile capable of improving the bearing strength more efficiently and effectively than in the past. .

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

  A method for constructing a cast-in-place concrete pile according to the present invention is a method for constructing a cast-in-place concrete pile having a columnar shaft portion and an expanded bottom portion obtained by expanding the tip portion of the shaft portion, An excavator is used to form an excavation hole in the shaft portion up to a predetermined depth in the ground, and an expanded bottom excavator for the shaft portion having a smaller diameter than the excavation hole in the shaft portion is formed in the excavation hole in the shaft portion. And the center axis of the bottom-excavating excavator is decentered by a predetermined amount with respect to the center axis of the shaft part, and the tip part of the excavation hole of the shaft part formed by preceding excavation is arranged. The hole wall is expanded by the excavator for expanding the bottom so as to form an excavation hole in the expanded bottom portion, and concrete is placed in the excavation hole in the shaft portion and the expanded bottom portion.

  In the method for constructing a cast-in-place concrete pile according to the present invention, a stabilizer that is a positioning convex portion that is coaxial with the central axis of the bottom-excavating excavator and projects below the excavating blade is provided at the tip of the bottom-excavating excavator. It is preferable that the stabilizer is pierced in a subsequent manner so as to pierce the ground at the bottom of the excavation hole.

  In the method for constructing a cast-in-place concrete pile according to the present invention, the ground immediately below the bottom surface of the excavation hole, which is the bottom of the pile, is improved in advance so that the uniaxial compressive strength is three times or more the pile supporting force. Is more desirable.

  In the method for constructing a cast-in-place concrete pile according to the present invention, the ground directly under the bottom surface of the excavation hole at an eccentric position arranged to pierce the stabilizer may be locally improved.

  The cast-in-place concrete pile of the present invention is a cast-in-place concrete pile having a columnar shaft portion and a bottom expanded portion formed by expanding the tip portion of the shaft portion, and the expanded bottom portion is the shaft in a plan view. It is constructed such that it has a convex arc portion protruding radially outward from a circular outer surface centering on the central axis of the portion.

  In the cast-in-place concrete pile construction method and cast-in-place concrete pile of the present invention, a cast-in-place concrete expanded pile with a high support strength capable of suitably supporting a very large column axial force such as a high-rise building is efficiently and effectively produced. It becomes possible to build.

It is a figure which shows the construction method of the cast-in-place concrete pile which concerns on one Embodiment of this invention. It is a figure which shows the case where a bottom expansion part is formed using the conventional bottom expansion excavator. It is a figure which shows the cast-in-place concrete pile which concerns on one Embodiment of this invention, and is a figure which shows the cast-in-place concrete pile at the time of performing bottom expansion excavation in three eccentric positions. It is a figure which shows the cast-in-place concrete pile which concerns on one Embodiment of this invention, and is a figure which shows the cast-in-place concrete pile at the time of performing bottom expansion excavation in four eccentric positions. It is a figure which shows the example of a change of the construction method of the cast-in-place concrete pile which concerns on one Embodiment of this invention. It is a figure which shows the conventional cast-in-place concrete pile (expanded bottom pile).

  Hereinafter, with reference to FIGS. 1-5, the construction method and the cast-in-place concrete pile which concern on one Embodiment of this invention are demonstrated.

  In the construction method of the cast-in-place concrete pile according to the present embodiment, the excavation machine such as an earth drill is used to excavate from the ground surface to a predetermined depth while filling with a stable liquid, and the cast-in-place concrete pile 1 ′ is abbreviated. The excavation hole 10 of the cylindrical shaft portion 2 having a constant diameter is formed (see FIG. 1). Next, a bottom-excavating machine (a bottom-extended machine such as a bottomed bucket) 5 connected to the lower end of the rod 4 is inserted into the excavation hole 10 of the shaft portion 2 and disposed at the tip, and the bottom-excavating machine 5 is expanded. By rotating around the central axis O1, the hole wall portion of the excavation hole 10 at the tip end is excavated at the bottom, and the excavation hole 11 of the broadened portion 3 having a substantially truncated cone shape is formed at the tip end portion. Then, concrete is placed in the excavation holes 10 and 11 so as to replace the stabilizing liquid using a tremy pipe, and a cast-in-place concrete pile 1 'is constructed. The cast-in-place concrete bottom-pile construction is completed by inserting reinforcing bars into the excavation holes 10 and 11, refilling the pile head side as needed, or constructing a pile head foundation.

  Here, as is conventionally known, the bottom-excavating excavator 5 has a bottom-expanding portion 3 (shaft portion) corresponding to the shaft portion 2 having a certain range of diameters, for example, φ2.1 to 3.0 m, as shown in FIG. The excavation hole 11) of the bottom expanded portion 3 can be formed corresponding to the two excavation holes 10.

  In the construction method of the cast-in-place concrete pile of this embodiment, it is utilized that the bottom expanded part 3 can be formed corresponding to the shaft part 2 having a diameter in a certain range.

  Specifically, in the construction method of the cast-in-place concrete pile according to the present embodiment, as shown in FIG. 1, the shaft portion 2 with a large shaft diameter such as 3.0 m is provided by an excavator (a shaft portion large-diameter bottom expander) 5. Next, for example, using a bottom-excavating machine (bottoming machine for small-diameter shaft diameter) 5 having a maximum bottom expansion diameter of 2.1 m or the like, the bottom expansion is performed with respect to the central axis O1 of the shaft portion 2. The center axis O2 of the excavator 5 (rod 4) is decentered, and the hole wall at the tip of the excavation hole 10 of the shaft portion 2 formed by the previous excavation is excavated at the bottom. Also, the bottom-excavating excavator 5 is disposed at a plurality of eccentric positions to perform bottom-expanding excavation, thereby forming the excavation holes 11 of the bottom expansion portion 3.

  Thereby, according to the construction method of the cast-in-place concrete pile of this embodiment, as shown in FIG.3 and FIG.4, the cast-in-place concrete pile (bottom-expanded pile) 1 'exceeding the maximum expanded diameter of the excavator 5 for expanded floor is shown. That is, it becomes possible to construct a cast-in-place concrete pile 1 ′ having a high bearing capacity. For example, in the construction method of the cast-in-place concrete pile according to the present embodiment, the pile is 1.3 times or more than the pile bottom area when the bottom widened portion 3 is formed as usual using the shaft large diameter widening machine 5. It is possible to form and construct the widened portion 3 having a bottom area.

  Here, FIG. 3 shows a cast-in-place concrete pile 1 ′ when bottomed excavation is performed at three eccentric positions, and FIG. 4 shows a cast-in-place concrete pile 1 ′ when bottomed excavation is performed at four eccentric positions. Each of the shapes is shown.

  As shown in FIGS. 3 and 4, the cast-in-place concrete pile 1 ′ of the present embodiment constructed as described above has an expanded bottom portion (pile bottom surface 1 a) centered on the central axis O <b> 1 of the shaft portion 2 in a plan view. It is constructed in a form provided with a convex arc portion (convex arc surface) 6 projecting radially outward from the circular outer surface. Thereby, the bottom expansion part 3 can improve the frictional resistance of the surface of a vertical part rather than the conventional truncated cone-shaped bottom expansion part 3 by the arc-shaped uneven | corrugated outer surface. Can be realized.

  On the other hand, the bottom surface of a pile conventionally formed by an excavator such as an earth drill has a mortar shape that gradually inclines upward from the central axis O1 toward the radially outer side. For this reason, for example, when the support layer G1 is gravel or the like, the bottom of the pile is touched when the excavating machine (bottoming machine for small-diameter shafts) 5 is decentered with the central axis O2 being excavated. The bottom portion of the excavator 5 in contact is not stable, the bottom ground collapses, or the bottom-excavating excavator 5 slides toward the central axis O1 side of the shaft portion 2 to cause misalignment, and the bottom is expanded by the small-diameter bottom expanding excavator 5 It is also conceivable that the excavation hole 11 of the portion 3 cannot be expanded.

  On the other hand, in this embodiment, as shown in FIG. 1, the bottom of the bottom-excavating machine 5 protrudes downward from the bottom surface coaxially with the central axis O <b> 1, and hits the bottom surface of the excavation hole 10. A stabilizer 7 which is a positioning convex portion for stabilizing the excavator 5 is provided. Further, the stabilizer 7 is formed so as to protrude downward from the excavation blade at the bottom of the excavator 5 for expanding the bottom. In addition, the stabilizer 7 of this embodiment is formed in the protrusion direction front-end | tip part in the taper shape and the sharp shape. Moreover, you may make it easy to stab in a downward ground by making it a drill or an auger shape.

  Thereby, even when the bottom surface of the excavation hole 10 that has been excavated in advance is formed in a mortar shape or the ground G is easily collapsed such as gravel, when the bottom expansion portion 3 is excavated by the subsequent excavation, the shaft portion 2 The bottom excavator 5 is stabilized by, for example, the stabilizer 7 being stuck into the bottom surface of the excavation hole 10 at a position eccentric from the central axis O1, and in this state, the excavation machine 5 for bottom expansion rotates around the central axis O2 and the excavation hole 10 is rotated. It is possible to drill the bottom of the hole wall. That is, the bottom expanding excavator 5 arranged at the eccentric position can perform the bottom expanding excavation without misalignment, and the cast-in-place concrete pile (the bottom expanded pile) exceeding the maximum bottom expanding diameter of the bottom expanding excavator 5 can be surely and suitably performed. It becomes possible to build 1 '.

  As mentioned above, although one Embodiment of the construction method of the cast-in-place concrete pile concerning this invention was described, this invention is not limited to said one Embodiment, It can change suitably in the range which does not deviate from the meaning. .

  For example, as shown in FIG. 5, the entire ground G directly under the pile bottom or the ground G where the stabilizer 7 pierces (the ground G directly under the pile bottom in the eccentric position) is improved using a deep ground improvement method or the like. (Ground improvement part 8) may be provided. In this case, when excavating the expanded bottom portion 3 by the subsequent excavation, the expanded excavator 5 can be further stabilized to perform the expanded bottom excavation of the hole wall of the excavation hole 10, which is more reliable and suitable. It becomes possible to construct a bottom expanded pile 1 ′ exceeding the maximum bottom expanded diameter of the bottom expanding excavator 5. In addition, this ground improvement part 8 is formed so that it may become a uniaxial compressive strength 3 times or more of pile supporting force, for example.

1 Conventional cast-in-place concrete pile (expanded bottom pile)
1 'Cast-in-place concrete pile (expanded bottom pile)
2 Shaft part 3 Expanded bottom part 4 Rod 5 Excavator 6 for expanding bottom Convex arc part 7 Stabilizer (positioning convex part)
8 Ground improvement part 10 Shaft excavation hole 11 Bottom excavation hole G Ground G1 Support layer

Claims (5)

A method of constructing a cast-in-place concrete pile having a columnar shaft portion and a bottom expanded portion formed by expanding the tip portion of the shaft portion,
Using the excavator for piles, the excavation hole of the shaft portion is pre-excavated to a predetermined depth of the ground, and formed,
Inserting an excavator for expanding the bottom of the shaft having a diameter smaller than that of the excavating hole of the shank into the tip of the excavating hole of the shank, and setting the central axis of the excavating machine for expanding the bottom to the central axis of the shank Placed by a predetermined amount,
The excavation hole of the bottom portion is formed by following the excavation so as to expand the hole wall of the tip portion of the excavation hole of the shaft portion formed by the preceding excavation with the excavator for bottom expansion,
A method for constructing a cast-in-place concrete pile, wherein concrete is placed in the excavation holes of the shaft portion and the expanded bottom portion. In the construction method of the cast-in-place concrete pile of Claim 1,
Provided at the tip of the bottom-excavating excavator is a stabilizer that is a positioning convex portion that is coaxial with the central axis of the bottom-excavating excavator and projects below the excavating blade;
A method for constructing a cast-in-place concrete pile, wherein the stabilizer is pierced by piercing the ground at the bottom of the excavation hole. In the construction method of the cast-in-place concrete pile of Claim 2,
A method for constructing a cast-in-place concrete pile, wherein the ground immediately under the bottom surface of the excavation hole, which is the bottom of the pile, is ground improved so as to have a uniaxial compressive strength of three times or more the pile supporting force. In the construction method of the cast-in-place concrete pile of Claim 3,
A method for constructing a cast-in-place concrete pile, wherein the ground immediately below the bottom surface of the excavation hole at an eccentric position disposed so as to pierce the stabilizer is locally improved. A cast-in-place concrete pile having a columnar shaft portion and an expanded bottom portion formed by expanding the tip portion of the shaft portion,
A cast-in-place concrete pile, wherein the bottom-up portion is constructed with a convex arc portion protruding radially outward from a circular outer surface centering on the central axis of the shaft portion in plan view.

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