Cast-in-place concrete pile

Abstract

To propose a cast-in-place concrete pile with little eccentricity of a pile core.SOLUTION: A cast-in-place concrete pile has a circular cross section and enlarged diameter sections 82, 84 at the middle and tip of a pile shaft, and comprises a concrete pile body having an intermediate enlarged diameter section 82 at the middle of the pile shaft and an enlarged base section 84 at the tip of the pile shaft, and a cylindrical protrusion 85 provided at a lower end of a center of the enlarged base section 84. The external dimension of a protrusion 85 is less than or equal to the external dimension of the pile shaft 81, 83. The lower limit of the external dimensions of the protrusion 85 is preferably the external diameter of a small-diameter pile hole 72 for the pile shaft, which is created as a guide hole for the pile shafts 81, 83.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a cast-in-place concrete pile having enlarged diameter portions in the middle and at the tip of the pile shaft. [Background technology]

[0002] By creating an enlarged section in the shaft of a cast-in-place concrete pile, its vertical bearing capacity and pull-out resistance can be increased. Concrete piles with an enlarged section have a large overturning moment, making them suitable for use as foundation piles for high-rise buildings and towers where pull-out resistance is a problem. Concrete piles with an enlarged section may also have both an enlarged base section at the bottom of the shaft and an intermediate enlarged section located midway along the shaft. Patent Documents 1 to 4 disclose methods for constructing concrete piles with enlarged diameter sections and devices such as an enlarged diameter bucket. Such concrete piles are constructed by using an excavation bucket to excavate a pile hole for the shaft section to a predetermined depth, and then using an enlarged diameter bucket to create a pile hole for the intermediate enlarged diameter section in the middle of the pile hole for the shaft section, and a pile hole for the enlarged bottom section at the tip of the pile hole for the shaft section. Patent Document 1 specifically discloses an enlarged diameter bucket for creating a pile hole for the intermediate enlarged diameter section and a pile hole for the enlarged bottom section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-159124 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-167450 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-227136 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-177794 Summary of the Invention [Problem to be solved by the invention]

[0004] In the concrete piles described in Patent Documents 1 to 4, the outer diameter of the enlarged portion is increased to increase the vertical bearing capacity and pull-out resistance and to shorten the pile length. However, increasing the outer diameter of the pile portion may cause the pile core to become eccentric. From this perspective, the present invention aims to propose a cast-in-place concrete pile with less eccentricity of the pile core. [Means for solving the problem]

[0005] The present inventors have discovered a method for constructing a cast-in-place concrete pile having expanded bottom sections in the middle and at the tip of the pile shaft, by first performing excavation using a small-diameter excavation bucket, then inserting an intermediate expansion bucket up to the height of the top of the excavated small-diameter pile hole, and expanding the bucket while rotating the expanding blades of the intermediate expansion bucket to construct the intermediate expansion section. Subsequently, using the small-diameter pile hole as a guide hole, a pile hole for the pile shaft is created up to the depth position of the tip of the pile using a large-diameter excavation bucket, and then expanding the expanding blades of the expanded bottom pile hole excavation bucket at the bottom of the pile hole while rotating the expanding blades to construct the expanded bottom section. This reduces the eccentricity of the pile hole, and thus the amount of eccentricity of the pile core can be reduced, leading to the present invention. In addition, a pile hole for the protrusion is provided at the lowest central end of the pile hole for the enlarged base at the tip of the pile, and the protrusion provided on the enlarged wing is inserted into this pile hole for the protrusion, which serves as a rotation fulcrum for the enlarged wing, stabilizing the rotation axis and suppressing eccentricity of the pile core.

[0006] The cast-in-place concrete pile of the present invention is a cast-in-place concrete pile with a circular cross-section that has expanded diameter sections in the middle of the pile shaft and at the tip, and is characterized in that it comprises a concrete pile body that has an intermediate expanded diameter section in the middle of the pile shaft and an expanded base section at the tip of the pile shaft, and a cylindrical protrusion provided at the central lower end of the expanded base section, and the outer dimensions of the protrusion are smaller than the outer dimensions of the pile shaft. The lower limit value of the outer dimension of the protrusion is preferably the outer diameter of a small-diameter pile hole for the pile shaft that is constructed as a guide hole for the pile shaft. [Effects of the Invention]

[0007] According to the present invention, a concrete pile with little eccentricity of the pile core can be constructed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a side view of an example of an intermediate expansion section excavation bucket according to the first embodiment, showing a state in which the expansion blades are in a closed position. [Figure 2] 1 is a side view of an example of an intermediate expansion section excavation bucket according to the first embodiment, showing a state in which the expansion blades are in an open position. FIG. [Figure 3] 3 is a view taken along the line III-III in FIG. 2, illustrating the configuration of the attachment portion of the inner main body, the shaft body, and the arm. FIG. [Figure 4] 10A to 10C are diagrams illustrating the movement of the arm in the guide groove of the inner main body when the position of the expansion wing is changed from a closed position to an open position. [Figure 5] 1A and 1B are plan views of the expansion blade, in which FIG. 1A shows the expansion blade in a closed position, and FIG. 1B shows the expansion blade in an open position. [Figure 6] FIG. 2 is a perspective view of the load transmitting body as seen obliquely from above. [Figure 7] FIG. 10 is a perspective view illustrating the function of transmitting a rotational force between the inner tube and the outer tube. [Figure 8] FIG. 2 is a side view of an example of a pile hole excavation bucket for a bottom expansion section used in the first embodiment, showing the expansion blades in an open position. [Figure 9] FIG. 1 is an explanatory diagram illustrating a method for constructing a cast-in-place concrete pile according to a first embodiment of the present invention. [Figure 10] FIG. 1 is an explanatory diagram illustrating a method for constructing a pile hole for a cast-in-place concrete pile, which is a reference example of the present invention. [Figure 11A] FIG. 1 is an explanatory diagram (1) illustrating a method for constructing a pile hole for a cast-in-place concrete pile according to a second embodiment of the present invention. [Figure 11B] FIG. 10 is an explanatory diagram (2) illustrating the pile hole construction method for a cast-in-place concrete pile according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a method for constructing a cast-in-place concrete pile, which involves first excavating with a small-diameter excavation bucket, inserting an intermediate expansion bucket into the small-diameter pile hole up to the height of its upper end, rotating the expansion blades of the intermediate expansion bucket to create an intermediate expansion section, and then using the small-diameter pile hole as a guide hole to create a pile shaft hole down to the depth of the pile tip using a large-diameter excavation bucket. Finally, at the bottom of the pile hole, rotating the expansion blades of the bottom expansion section pile hole excavation bucket to create an expansion section. The first embodiment of the method for constructing a cast-in-place concrete pile is a method for constructing an intermediate expansion section 82 using an intermediate expansion section excavation bucket 50 equipped with a hydraulic unit 56. The second embodiment is a method for constructing a cast-in-place concrete pile using a mechanical intermediate expansion section excavation bucket 59 without a hydraulic unit 56. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Each drawing is merely a schematic illustration to allow a sufficient understanding of the present invention. Therefore, the present invention is not limited to the illustrated examples. In each drawing, common or similar components are designated by the same reference numerals, and redundant explanations thereof will be omitted. The cast-in-place concrete pile of each embodiment described below is a multi-stage pile provided with both an intermediate enlarged section and an enlarged bottom section. The method for constructing a cast-in-place concrete pile of this embodiment includes a pile hole creation step of creating a pile hole in the ground that has a pile hole for the intermediate enlarged section and a pile hole for the enlarged bottom section, and a concrete pouring step of pouring concrete into this pile hole for the pile shaft. First, the configurations of the intermediate expansion section excavation bucket 50 (Figs. 1 and 2) used for constructing the pile hole for the intermediate expansion section and the pile hole excavation bucket 69 (Fig. 8) used for constructing the pile hole for the expanded bottom section will be described. After that, the pile hole construction process of this embodiment will be described.

[0010] [Mechanical Expanding Bucket with Hydraulic Mechanism According to the Embodiment] FIG. 1 is a side view of an example of an excavation bucket for an intermediate expansion section used in an embodiment of the present invention. 2 is a diagram showing the expanded diameter blade in a closed position, and FIG. 1, the intermediate expansion section excavation bucket 50 has a hydraulic unit 56 and a mechanical expansion bucket 59. The hydraulic unit 56 includes a load transmission body 90, an outer pipe 110 disposed inside the load transmission body 90, an inner pipe 95 disposed inside the outer pipe 110, and a hydraulic jack 94 disposed inside the inner pipe 95. The mechanical expansion bucket 59 is detachably attached to the hydraulic unit 56.

[0011] The inner tube 95 is configured to include a first upper cover 91 and a first cylindrical body 92 that are circular in plan view. The lower end of the kelly bar 30 is fixed to the upper surface 91a of the first upper cover 91. The hydraulic jack 94 includes a cylinder 94a and a piston rod 94b that slides within the cylinder 94a. The lower surface 91b of the first upper cover 91 and the cylinder 94a are fixed by bolts. The outer tube 110 includes a lower cover 111 that is circular in plan view and a second cylindrical body 112. The upper surface 111a of the lower cover 111 and the piston rod 94b are fixed by bolts. The second cylindrical body 112 is disposed on the outer periphery of the first cylindrical body 92. The mechanical expanding bucket 59 comprises a cylindrical outer body 55, a cylindrical inner body 54 disposed inside the outer body 55, a shaft 53 that slides inside the inner body 54 and is fixed to the outer pipe 110, an arm 52 attached to the shaft 53, and an expanding blade 51 attached to the tip of the arm 52. 2, a guide groove 54a is formed in the inner main body 54, which is opened in a direction inclined (at an inclination angle θ1) with respect to the axial direction L1 of the inner main body 54. The arm 52 is guided by this guide groove 54a, so that the diameter expansion blade 51 is configured to assume a closed position 51a (FIG. 1) and an open position 51b (FIG. 2).

[0012] As shown in Fig. 3, a key 52a is engaged with a cylindrical shaft 53, extending in a direction perpendicular to the longitudinal direction of the shaft 53 and penetrating the shaft 53. End covers 52b are attached to both ends of the key 52a. A portion of the end cover 52b is inserted into a guide groove 54a in the inner body 54. Furthermore, a universal joint 52c is attached to the end cover 52b, and a connecting member 52d is attached to the universal joint 52c. The tip of the connecting member 52d is rotatably attached to two diameter expansion blades 51 of a mechanical diameter expansion bucket 59 (FIG. 2).

[0013] FIG. 4 is an explanatory diagram illustrating the movement of the arm in the guide groove of the inner main body when the position of the expansion wing is changed from the closed position to the open position. 4(a) to 4(c) all show a state in which the key 52a constituting the arm 52 penetrates the guide groove 54a and faces the front of the page at the center t / 2 of the inner body 54 having an outer diameter t. Also, FIG. 4(a) shows the position of the key 52a relative to the guide groove 54a when the expansion wing 51 is in the closed position 51a (FIG. 1). FIG. 4(b) shows the expansion wing 51 in the middle of transition from the closed position 51a (FIG. 1) to the open position 51b (FIG. 2). Furthermore, FIG. 4(c) shows the position of the key 52a relative to the guide groove 54a when the expansion wing 51 is in the open position 51b (FIG. 2). The shaft 53 (FIG. 3) with which the key 52a engages is pushed downward by the extension of the piston rod 94b of the hydraulic jack 94 via the lower cover 111 of the outer tube 110. As is clear from looking at FIGS. 4(a) to 4(c) in order, the pushed-down key 52a moves vertically downward in the X2 direction (FIG. 4(b)), while maintaining its position at position t / 2, which is the center position of the inner body 54.

[0014] 4(b), the key 52a moves downward h1 along the guide groove 54a extending in the diagonal direction while maintaining its position in a side view, whereby the horizontal component S1 of the pressing force S that the side surface of the guide groove 54a receives from the downward moving key 52a causes the inner main body 54 to rotate in the X3 direction. At this time, the diameter expansion wing 51 assumes a partially open position. As shown in FIG. 4(c), when the key 52a moves further downward by h2 along the guide groove 54a and reaches the lower end of the guide groove 54a, the horizontal component S1 of the pressing force S that the side surface of the guide groove 54a receives from the downward moving key 52a causes the expansion blade 51 to assume the open position 51b, which is the fully open state shown in FIG. 2. In this way, by operating the hydraulic jack 94 (FIG. 1), the diameter expansion blade 51 can be changed from the closed position 51a (FIG. 1) to the open position 51b (FIG. 2). Also, as shown in FIG. 1, the weight of the mechanical diameter expansion bucket 59 is supported in the Z1 direction by the load transmission body 90, and the load transmission The force of the body 90 is transmitted in the Z2 direction via the rollers 99 and the inner tube 95 to the kelly bar 30 fixed to the inner tube 95. Therefore, when opening or closing the diameter expansion vane 51, even in a state where there is no reaction force from the ground, the reaction force generated when the hydraulic jack 94 is operated is transmitted to the kelly bar 30, thereby enabling the opening and closing of the diameter expansion vane 51.

[0015] FIG. 5 is a plan view of the expansion blade, in which (a) shows the expansion blade in a closed position, and (b) shows the expansion blade in an open position. As shown in Figure 5(a), the two expansion wings 51 are arc-shaped when viewed from above, and in the closed position 51a shown in the figure, the tip of each expansion wing 51 is engaged with a wing stopper 57, preventing the expansion wings 51 from rotating further inward than in the state shown in the figure. On the other hand, as shown in FIG. 5(b), in the illustrated open position 51b in which the expansion blades 51 are opened in the X4 direction, each expansion blade 51 rotates in the Y4 direction in response to the rotation of the kelly bar 30 (FIG. 1), and the excavated soil D is effectively scooped up by the expansion blades 51, which are arc-shaped in plan view, and is transported in the rotation direction of the expansion blades 51.

[0016] 1, shaft 53 is fixed to the lower surface 111b of lower cover 111 of outer pipe 110. Furthermore, protrusion 58 consisting of cylindrical portion 58a and conical portion 58b is formed at the lower end of outer main body 55. Protrusion 58 is attached so as to be able to open and close freely, and when opened, excavated earth and sand stored inside outer main body 55 is carried out. 1, the load transmitting body 90 includes a second upper cover 97 that is circular in plan view and a third cylindrical body 98. A kelly bar opening 97a, through which the kelly bar 30 is inserted, is formed in the center of the second upper cover 97. The second upper cover 97 is placed on the upper surface 91a of the first upper cover 91 of the inner pipe 95 via rollers 99. A stabilizer 120 that controls the attitude of the mechanical expanding bucket 59 in the pile hole is disposed above the mechanical expanding bucket 59, and the third cylindrical body 98 is fixed to the stabilizer 120 via a connecting member 115.

[0017] FIG. 6 is a perspective view of the load transmitting body 90 shown in FIG. 1, viewed obliquely from above. A plurality of rollers 99 are rotatably attached to an upper surface 91a of the first upper cover 91 of the inner pipe 95 at intervals in the circumferential direction of the first upper cover 91. Furthermore, a second upper cover 97 of the load transmission body 90 is placed on the first upper cover 91 via a plurality of rollers 99. In this way, by placing the second upper cover 97 on the first upper cover 91 via a plurality of rollers 99, the load transmission body 90 can be rotatably placed on the inner pipe 95. Therefore, when the load transmission body 90, which directly supports the weight of the mechanically expanding bucket 59, rotates relative to the inner pipe 95, excessive frictional force can be generated between the inner pipe 95 and the load transmission body 90, which would cause damage to both.

[0018] FIG. 7 is a perspective view illustrating the function of transmitting a rotational force between the inner tube and the outer tube. A plurality of engaging protrusions 96 extending in the axial direction L2 of the first cylindrical body 92 are provided on the outer periphery of the first cylindrical body 92 at intervals in the R1 direction, which is the circumferential direction of the first cylindrical body 92. Meanwhile, a plurality of engaged protrusions 113 extending in the axial direction L2 of the second cylindrical body 112 are provided on the inner periphery of the second cylindrical body 112 of the outer tube 110. These engaged protrusions 113 are provided in pairs in a plurality of sets, and an engaging protrusion 96 is disposed between the engaged protrusions 113 in each set. With this configuration, the outer tube 110 is slidable relative to the inner tube 95 in the Y3 direction along the axial direction L2, and when the inner tube 95 rotates in the Y4 direction in response to the rotation of the kelly bar 30, the engaging protrusion 96 is able to engage with either of the engaged protrusions 113 on the left or right side thereof.

[0019] 2, the rotation torque generated when the kelly bar 30 rotates in the Y1 direction causes the inner tube 95 to rotate in the Y2 direction, and the engaging projection 96 engages with the engaged projection 113 (FIG. 7), causing the outer tube 110 to engage with the inner tube 95 and rotate in the Y3 direction. Furthermore, the rotation of the outer tube 110 causes the shaft 53 fixed to the outer tube 110 to rotate, and the shaft 53 is configured The entire mechanical expanding diameter bucket 59, which is a constituent element of the kelly bar 30, rotates in the Y4 direction. In this manner, the rotational torque of the kelly bar 30 is transmitted to the mechanical expanding diameter bucket 59 via the inner pipe 95 and the outer pipe 110. 2, the expansion blade 51 has a shape in side view in which an upper inclined blade 51c having a triangular shape in side view, a rising blade 51d having a rectangular shape in side view, and a lower inclined blade 51e having an inverted triangular shape in side view are connected, and multiple cutting bits 51f are attached to the side ends of each part. Note that all of the cutting bits 51f may be fixed bits fixed to the side ends, or may be a combination of fixed bits and rotatable rotating bits. Furthermore, the expansion blade 51 may not have the downward inclined blade 51e as in the illustrated example, but may have a shape in side view in which the upper inclined blade 51c and the rising blade 51d are connected.

[0020] 2, part of the reaction force generated when the hydraulic jack 94 is operated is transmitted to the mechanical diameter expansion bucket 59 in the Z3 direction via the inner pipe 95 to which the cylinder 94a is fixed and via the load transmission body 90 placed above the inner pipe 95. Therefore, transmission of an excessive reaction force to the kelly bar 30 when the hydraulic jack 94 is operated is suppressed. The protrusion 58 is made up of a cylindrical portion 58a and a conical portion 58b, and is provided on the lower part of the outer main body 55. The diameter φ3 of the cylindrical portion 58a is approximately the same as the diameter φ2 of the outer main body 55.

[0021] FIG. 8 is a side view of an example of a pile hole excavation bucket for a bottom expansion portion used in an embodiment of the present invention, showing a state in which the diameter expansion blades are in an open position. The pile hole boring bucket 69 for the bottom expansion section comprises an outer pipe 110a, an inner pipe 95a, a shaft 63, an inner body 64, an outer body 65, expansion blades 61, and protrusions 68. Here, similar to the outer pipe 110 and inner pipe 95 shown in FIG. 7, a plurality of engaging protrusions 96 (FIG. 7) are formed on the outer periphery of the inner pipe 95a, and a plurality of engaged protrusions 113 (FIG. 7) are formed on the inner periphery of the outer pipe 110. The outer pipe 110a is fixed to the outer body 65 via a stabilizer 120. The lower end of the kelly bar 30 is fixed to the upper surface of the inner pipe 95, and the shaft 63 is fixed to the lower surface of the inner pipe 95.

[0022] As the kelly bar 30 rotates, the inner tube 95 rotates, and the expansion blade 61 rotates via the outer tube 110 and the outer main body 65. Furthermore, when the protrusion 68 is fixed to the bottom of the hole and the inner main body 64, the outer main body 65, and the expansion blade 61 do not move vertically, if the kelly bar 30 is pushed down, the shaft 63 and the key 62a are also pushed down. As a result, the inner main body 64 rotates in the X3 direction (FIGS. 4(b) and 4(c)), and the expansion blade 61 is expanded by the arm 52. The protrusion 68 is composed of a cylindrical portion 68a and a conical portion 68b, similar to the protrusion 58 (Fig. 1). In other words, the pile hole excavation bucket 59 for the bottom expansion section has the same configuration as the intermediate expansion section excavation bucket 50 (Figs. 1 and 2), but does not have the hydraulic unit 56. In addition, the expansion wing 61 has an upper inclined wing 61c that is triangular in side view and a rising wing 61d that is rectangular in side view, but does not have anything equivalent to the lower inclined wing 51e (Fig. 1).

[0023] (First embodiment) FIG. 9 is an explanatory diagram illustrating a method for constructing a cast-in-place concrete pile according to the first embodiment of the present invention. In step s1 of Fig. 9, a cylindrical casing 21 with a diameter φ1 (for example, φ1 = 3.2 m) is inserted into the ground from the ground surface GL to a depth D2, while the inside of the casing 21 is excavated using a full-circle rotary excavator. In step s2 of Fig. 9, a power jack (not shown) is used to pull out the casing 21 to a depth D16 shallower than the foundation bottom level (the position of depth D15 (s11)). In step s3 of Fig. 9 (the "first step" in the claims), a pile hole 71 for the first pile shaft with a diameter φ2 (for example, φ2 = 3 m) and a depth D12 is created using a large-diameter excavation bucket 42 (Fig. 11A (s1)). The pile hole 71 for the first pile shaft is formed in a soft layer (for example, If a silt layer 12) has accumulated, excavation should be carried out up to the top of the layer. In step s4 of Figure 9 ("second step" including "step of creating small-diameter pile hole for pile shaft" in the claims), a small-diameter pile hole 72 for the pile shaft with a diameter of φ3 (φ3<φ2) (for example, φ3=2.2m) is created using a small-diameter excavation bucket 41 (Figure 11A(s2)). Here, the length of the small-diameter pile hole 72 for the pile shaft is shorter by D13 (for example, D13=50cm) than the second pile hole 74 for the pile shaft. This is to avoid damaging the supporting layer at the tip of the pile.

[0024] In step s5 of Figure 9 (the "second step" in the claims), the upper part of the small-diameter pile hole 72 for the pile shaft is enlarged by the large-diameter excavation bucket 42 (Figure 11A (s1)). In other words, as shown by the arrow, the pile hole 71 for the first pile shaft is extended. At this time, for example, the pile hole 71 for the first pile shaft is embedded deeper than D14 (for example, 1 m) from the lower end of the silt layer 12. In step s6 of FIG. 9 (the "second step" including the "intermediate enlarged diameter section creating step" in the claims), as will be explained in FIG. 10 (s2) of the reference example described later, the intermediate enlarged diameter section excavation bucket 50 (FIGS. 1 and 2) is disposed at the bottom of the pile hole 71 for the first pile shank. At this time, the protrusion 58 (FIGS. 1 and 2) is inserted into the top of the small-diameter pile hole 72 for the pile shank. This positions the intermediate enlarged diameter section excavation bucket 50 (FIGS. 1 and 2). Then, the enlarged diameter blades 51 of the intermediate enlarged diameter section excavation bucket 50 are rotated and expanded to create the pile hole 73 for the intermediate enlarged diameter section with an intermediate enlarged diameter φ4 (for example, φ4 = 5.3 m). That is, in this embodiment, the intermediate enlarged diameter section creating step (s6) is performed after the small-diameter pile hole creating step (s4) for the pile shank. Then, the expansion wing 61 is closed, and the intermediate expansion section excavation bucket 50 is pulled up to the ground (not shown). In step s7 of Figure 9 (the "third step" in the claims), the diameter of the small-diameter pile hole 72 for the pile shaft is enlarged from φ3 to φ2 (φ2 > φ3) by the large-diameter excavation bucket 42 (Figure 11A (s1)). The tip of the large-diameter excavation bucket 42 is extended to a depth D13 below the lower end surface of the small-diameter pile hole 72 for the pile shaft. This creates a second pile hole 74 for the pile shaft. As described above, this is a method for constructing a cast-in-place concrete pile by creating a pile hole by two-stage excavation using two types of excavation buckets with different diameters (a small-diameter excavation bucket 41 that excavates first, and a large-diameter excavation bucket 42 that is used during subsequent excavation, with the pile hole 71 for the first pile shaft serving as a guide hole). This is also a cast-in-place concrete pile created using a pile hole created by the two-stage excavation.

[0025] In step s8 of Fig. 9 (the "projection hole making step" in the claims), a projection hole 76 having a diameter of φ5 (for example, φ5=φ3<φ2 (for example, φ5=φ3=2.2m)) is made by the small-diameter excavation bucket 41 (Fig. 11A(s2)). Here, φ5=φ3, but a different diameter may be used. In step s9 of Fig. 9 (the "fourth step" in the claims), as will be explained in Fig. 10 (s5) of the reference example described later, the pile hole excavation bucket 69 for the enlarged bottom portion (Fig. 8) is placed at the bottom of the pile hole 74 for the second pile shaft portion. At this time, the protrusion 68 (Fig. 8) is inserted into the pile hole 76 for the protrusion portion. This positions the pile hole excavation bucket 69 for the enlarged bottom portion. Then, the expansion blade 61 of the pile hole excavation bucket 69 for the enlarged bottom portion (Figs. 8, 10 (s6)) is rotated and expanded to create the pile hole 75 for the enlarged bottom portion with an expansion diameter of φ6 (for example, φ6 = 5.3 m). At this time, the combination of the pile hole 76 for the protrusion portion and the protrusion 68 becomes the rotation fulcrum of the expansion blade 61. This rotation fulcrum suppresses eccentricity of the pile core. Then, the pile hole excavation bucket 69 for the enlarged bottom portion is taken out from the small-diameter pile hole 72 for the pile shaft portion (not shown).

[0026] In step s10 of Fig. 9, the bottom of the pile hole 75 for the enlarged bottom is scraped and slime is removed. Here, the pile hole 76 for the protrusion is enlarged to a diameter of φ7 (for example, φ7 = 3 m). By enlarging the diameter, it is possible to increase the amount of slime that can be received. The slime is a mixture of bentonite mud used to protect the excavation wall surface and particles of excavated soil that settle at the bottom of the hole. In step s11 of Fig. 9, reinforcing bars 25 are inserted from the expanded bottom portion to the foundation bottom level (the position of depth D15), and furthermore, structural columns 26 are erected to the top of the reinforcing bars (i.e., to a position deeper than the foundation bottom level). In other words, the top of the reinforcing bars 25 and the bottom of the structural columns 26 overlap. In step s12 of Figure 9 (the "fifth step" in the claims), concrete is poured into the pile hole 71 for the first pile shank, the pile hole 73 for the intermediate enlarged diameter section, the pile hole 74 for the second pile shank, and the pile hole 75 for the enlarged bottom section. This constructs a cast-in-place concrete pile 100. The cast-in-place concrete pile 100 is a reinforced concrete pile in which the first pile shank 81, the intermediate enlarged diameter section 82, the second pile shank 83, and the enlarged bottom section 84 are continuously constructed. The enlarged bottom section 84 includes a protrusion 85. The outer diameter φ7 of the protrusion 85 is equal to or greater than φ5 (e.g., φ5 = φ3 < φ2) and equal to or less than the outer diameter φ2 of the second pile shank 83.

[0027] As explained above, according to this embodiment, the ground around the small-diameter pile hole 72 for the pile shaft, which has a diameter of φ3, is excavated, and the small-diameter pile hole for the pile shaft is used as a guide hole to expand the diameter to φ2, thereby creating the second pile hole 74 for the pile shaft. This reduces the eccentricity of the pile hole. Furthermore, the protrusion 58 (Figs. 1 and 2) is inserted into the upper part of the small-diameter pile hole 72 for the pile shaft. This serves as the rotation fulcrum for the expansion wing 51. Furthermore, the protrusion 68 (Fig. 8) is inserted into the protrusion hole 76 for the protrusion. This serves as the rotation fulcrum for the expansion wing 61. Positioning by the rotation fulcrum stabilizes the rotation axis, thereby suppressing eccentricity of the pile core.

[0028] (Reference example of the first embodiment) In the first embodiment, the ground around the small-diameter pile hole 72 for the pile shaft with a diameter of φ3 is excavated, and the small-diameter pile hole for the pile shaft is used as a guide hole to expand the diameter to φ2. Using a reference example in which the pile hole 70 for the pile shaft with a diameter of φ2 is excavated in one go, the expansion of the pile hole 73 for the intermediate expansion section and the pile hole 75 for the expansion bottom section will be further explained. Fig. 10 is an explanatory diagram illustrating a method for constructing pile holes for cast-in-place concrete piles according to a reference example of the present invention. With reference to Fig. 10, a method for constructing pile holes for burying multi-tiered piles at a predetermined depth (D1) from the ground surface (GL) or the foundation bottom level will be described.

[0029] In step s1 of Figure 10, the shaft (the pile hole 70 for the pile shaft) is excavated using the large-diameter excavation bucket 42 while injecting the stabilizing fluid 22. The stabilizing fluid 22 is, for example, bentonite containing a water-soluble polymer, and is used to prevent ground collapse and ensure safe construction. The excavation is continued beyond the depth required to create the pile hole 73 for the intermediate enlarged diameter section, to a position where the pile hole 75 for the enlarged bottom section will be created. Near the ground surface GL, a cylindrical casing 21 is placed in the ground, and excavation is continued using the large-diameter excavation bucket 42 to a depth D2. In step s2 of Fig. 10, the intermediate expansion section excavation bucket 50 is installed at a predetermined depth inside the pile hole 70 for the pile shaft section. At this time, the intermediate expansion section excavation bucket 50 is suspended by the kelly bar 30 in a closed position 51a in which the expansion wings 51 are closed, and is inserted into the pile hole 70 for the pile shaft section. The predetermined depth D3 is the position of the lower end of the intermediate expansion section excavation bucket 50, and is slightly deeper than the bottom of the pile hole 73 for the intermediate expansion section.

[0030] In step s3 of Fig. 10, the expansion blades 51 of the intermediate expansion section excavation bucket 50 are rotated and gradually expanded to the open position 51b. This creates the pile hole 73 for the intermediate expansion section. More specifically, the expansion blades 51 are rotated by rotating the kelly bar 30, which has a fixed depth. In addition, the hydraulic jack 94 presses the shaft 53 downward with a force F1, thereby expanding the expansion blades 51 from the closed position (51a (s2)) to the open position (51b (s3)). At this time, a reaction force F2 is applied to the hydraulic jack 94. In steps s2 to s3, the expansion blades 51 scrape out the soil, creating the pile hole 73 for the intermediate expansion section, and soil 15 is deposited at the bottom of the pile hole 70 for the pile shaft section. Although not shown, after step s3 is completed, the expansion wing 51 of the intermediate expansion section excavation bucket 50 is set to the closed position 51a, and the intermediate expansion The excavation bucket 50 is raised. In step s4 of Fig. 10, the large diameter excavation bucket 42 is again attached to the kelly bar 30, and the accumulated earth and sand 15 is collected. At this time, the large diameter excavation bucket 42 excavates a depth H4 deeper than the depth D1 (s1). In addition, the conical lower shape of the large diameter excavation bucket 42 creates a conical recess 70a at the bottom of the pile hole 70 for the pile shaft. The pile hole 73 for the intermediate expansion section has a rising height H1 determined by the shape of the expansion wing 51 (particularly, the rising section wing 51d (Fig. 2)).

[0031] In step s5 of Fig. 10, the pile hole excavating bucket 60 for the enlarged bottom portion, which is fixed to the lower end of the kelly bar 30, is placed at the bottom of the pile hole 70 for the pile shaft portion. At this time, the enlarged blade 61 is in the closed position 61a. In addition, the protrusion 68 of the pile hole excavating bucket 69 for the enlarged bottom portion is inserted into the conical recess 70a. This positions the pile hole excavating bucket 69 for the enlarged bottom portion, and prevents the pile core (center of rotation) from becoming eccentric. In step s6 of Fig. 10, the expansion blades 61 are expanded while the bucket 69 for excavating the pile hole for the expansion bottom portion is rotated. This creates the pile hole 75 for the expansion bottom portion. Specifically, since the protrusion 68 of the bucket 69 for excavating the pile hole for the expansion bottom portion has reached the bottom of the ground, the kelly bar 30 is pushed down to lower the shaft 63 (Fig. 8), and the expansion blades 61 are expanded to the open position 61b. At this time, the protrusion 68 receives a reaction force F3 from the bottom. Thereafter, the bucket 69 for excavating the pile hole for the enlarged bottom portion is removed from the pile hole for the enlarged bottom portion 75. Then, although not shown in the drawings, concrete is poured into the pile hole for the first pile shaft portion, the pile hole for the intermediate enlarged diameter portion 73, the pile hole for the second pile shaft portion, and the pile hole for the enlarged bottom portion 75 to construct a cast-in-place concrete pile.

[0032] As described above, in this reference example, the protrusion 68 of the pile hole excavating bucket 69 for the enlarged bottom portion is inserted into the conical recess 70a (step s5). As a result, the protrusion 68 serves as a fulcrum when the pile hole excavating bucket 69 for the enlarged bottom portion is rotated. In other words, the pile hole excavating bucket 69 for the enlarged bottom portion is positioned, and eccentricity of the pile core is suppressed.

[0033] (Second embodiment) In the first embodiment, an intermediate expansion section excavation bucket 50 having a hydraulic unit 56 was used, but a mechanical intermediate expansion section excavation bucket 59 (Figures 1 and 2) that does not have a hydraulic unit 56 can also be used. 11A and 11B are explanatory diagrams illustrating a method for forming a pile hole for a cast-in-place concrete pile according to a second embodiment of the present invention. In step s1 of Fig. 11A (the "first step" in the claims), a casing 21 with a diameter of φ1 is inserted, as in Fig. 9 (s1) of the first embodiment, and then a pile hole 71 for the first pile shaft with a diameter of φ1 is created using a large-diameter excavation bucket 42 with a diameter of φ2, as in Fig. 9 (s3, s7). The pile hole 71 for the first pile shaft is excavated up to the lower end of the pile hole 73 for the intermediate enlarged diameter portion (s5). In step s2 of FIG. 11A, the small diameter excavation bucket 41 having a diameter of φ3 (φ3<φ2) is used to create the pile hole 76 for the protrusion at the lower end of the pile hole 71 for the first pile shaft.

[0034] In step s3 of Figure 11A, the mechanical expansion bucket 59 with an outer diameter φ3 is inserted up to the lower end of the pile hole 71 for the first pile shaft portion. As a result, the protrusion 58 is inserted into the pile hole 76 for the protrusion portion. Here, the mechanical expansion bucket 59 is the intermediate expansion portion excavation bucket 50 (Figures 1 and 2) without the hydraulic jack 94. In other words, the kelly bar 30 lifts up the shaft 53 (Figures 1 and 2). In step s4 of FIG. 11A (the "second step" including the "intermediate expanded diameter portion forming step" in the claims), the kelly bar 30 is rotated and pushed down, whereby the shaft 53 (FIGS. 1 and 2) of the mechanically expanded diameter bucket 59 is rotated and pushed down. 4 is repeated, and the diameter expansion blade 51 is gradually expanded while rotating, thereby creating a pile hole 73 for the intermediate expansion portion. In step s5 of Fig. 11A ("second step" including "step of creating small-diameter pile hole for pile shaft" in the claims), a small-diameter pile hole 72 for the pile shaft with a diameter of φ3 is created to the depth of the expanded bottom portion by the small-diameter excavation bucket 41. That is, in this second embodiment, unlike the first embodiment (s4, s6 in Fig. 9), a step of creating a small-diameter pile hole for the pile shaft 72 (s5) is carried out after the step of creating an intermediate expanded diameter portion (s4) of creating a pile hole 73 for the intermediate expanded diameter portion.

[0035] In step s6 of Figure 11B (the "third step" in the claims), the small-diameter pile hole 72 for the pile shaft, which has a diameter of φ3, is enlarged by the large-diameter excavation bucket 42 to create a pile hole 74 for the second pile shaft, which has a diameter of φ2 (φ2 > φ3). At this time, a recess (pile hole 76 for the protrusion) with a diameter of φ3 is created at the bottom of the pile hole 74 for the second pile shaft, leaving a small portion of the tip (pile bottom) of the small-diameter pile hole 72 for the pile shaft. By creating the thin small-diameter pile hole 72 for the pile shaft and then creating the thick pile hole 74 for the second pile shaft, the eccentricity of the pile shaft is reduced. In step s7 of Figure 11B, the kelly bar 30 is used to place the pile hole boring bucket 60 for the enlarged bottom portion, having an outer diameter of φ3, at the bottom of the pile hole 74 for the second pile shank portion via the pile hole 71 for the first pile shank portion and the pile hole 73 for the intermediate enlarged diameter portion. At this time, the tip of the kelly bar 30 is fixed to the shaft 63 of the pile hole boring bucket 60 for the enlarged bottom portion. In addition, the protrusion 68 (Figure 8) is inserted into the pile hole 76 for the protrusion portion. In step s8 of Fig. 11B (the "fourth step" in the claims), the kelly bar 30 is rotated and pushed down. That is, the shaft 63 of the bucket 60 for excavating the pile hole for the enlarged bottom portion is rotated and pushed down. These steps s7 and s8 are repeated, and the diameter expansion blade 61 is gradually expanded while rotating, thereby creating the pile hole for the enlarged bottom portion 75.

[0036] In step s9 of Figure 11B, the eccentric pump 24 sucks up the slime and sediment that has settled at the bottom. At this time, the kelly bar 30 is moved parallel to the bottom and rotated to clean the entire bottom. Although not shown, the eccentric pump 24 includes, for example, a pump section, a propeller-shaped agitator that agitates the slime or sediment, and a skirt section that covers the rotation range of the agitator and the suction port of the pump section. This skirt section is formed in an eccentric truncated cone shape. In step s10 of Fig. 11B (the "fifth step" in the claims), reinforcing bars 25 are placed inside the pile hole 71 for the first pile shaft portion, the pile hole 73 for the intermediate enlarged diameter portion, the pile hole 74 for the second pile shaft portion, and the pile hole 75 for the enlarged bottom portion. Thereafter, concrete is poured into the pile hole 71 for the first pile shaft portion, the pile hole 73 for the intermediate enlarged diameter portion, the pile hole 74 for the second pile shaft portion, and the pile hole 75 for the enlarged bottom portion.

[0037] As described above, according to this embodiment, the pile hole 73 for the intermediate expansion section can be created using the mechanical expansion bucket 59 that does not have a hydraulic jack 94. In addition, the pile hole 76 for the protrusion section created at the bottom of the pile hole 71 for the first pile shaft section and the protrusion section 58 of the mechanical expansion bucket 59 serve as a rotation fulcrum. Positioning by the rotation fulcrum stabilizes the rotation axis.

[0038] [Variations] (1) In steps s6 to s9 (Fig. 9) of the first embodiment, a small-diameter pile hole 72 for the pile shaft with a diameter of φ3 is excavated (s6), a pile hole 74 for the second pile shaft with a diameter of φ2 (φ2>φ3) is excavated by expanding the diameter (s7), and a pile hole 76 for the protrusion with a diameter of φ5=φ3 is excavated at the tip. Instead of this, as in steps s5 (Fig. 11A) and s6 (Fig. 11B) of the second embodiment, the small-diameter pile hole 72 for the pile shaft and the pile hole 76 for the protrusion with a diameter of φ3 may be excavated from the beginning, and the small-diameter pile hole 72 for the pile shaft with a diameter of φ2 may be expanded up to the diameter of φ2 just before the pile hole 76 for the protrusion, thereby excavating the small-diameter pile hole 72 for the pile shaft with a diameter of φ2. (2) In s3 and s4 of the second embodiment (FIG. 11A), the hydraulic unit 56 is not provided. Although the intermediate expansion section excavation bucket 59 is used, the intermediate expansion section excavation bucket 50 (FIGS. 1 and 2) having the hydraulic unit 56 may also be used. (3) In the second embodiment, the small-diameter pile hole 72 for the pile shaft with a diameter of φ3 is created (s5 (Fig. 11A)), and the pile bottom of the small-diameter pile hole 72 for the pile shaft is left slightly widened to create the pile hole 74 for the second pile shaft, and the small-diameter pile hole for the pile shaft with a diameter of φ3 left at the bottom is used as the pile hole 76 for the protrusion (s6 (Fig. 11B)). Instead of this, as in the first embodiment, the small-diameter pile hole 72 for the pile shaft with a diameter of φ3 is widened to create the pile hole 74 for the second pile shaft with a diameter of φ2 (s7), and the pile hole 76 for the protrusion with a diameter of φ5 = φ3 is created at the tip of the pile hole 74 for the second pile shaft. (4) Instead of the intermediate expanding bucket 50 having a hydraulic unit in the first and second embodiments, an intermediate expanding bucket incorporating a hydraulic jack may be used. [Explanation of symbols]

[0039] 30 Kelly 41 Small diameter excavation bucket 42 Large diameter excavation bucket 50 Intermediate expansion section excavation bucket 51,61 Expanded diameter wing 51a,61a Closed position 51b,61b Open position 53,63 Axial body 54,64 Inner body 55,65 Outer body 56 Hydraulic unit 58,68 Protrusion 59 Mechanical expanding bucket (mechanical intermediate expanding bucket) 69 Pile hole digging bucket for enlarged bottom 70 Pile hole for pile shaft 71 Pile hole for 1st pile shaft 72 Small diameter pile hole for pile shaft 73 Pile hole for intermediate expanded diameter section 74 Pile hole for second pile shaft 75 Pile holes for enlarged bottom 76 Pile hole for protrusion 80 Pile shaft 81 1st pile shaft section 82 Intermediate expansion section 83 2nd pile shaft section 84 Enlarged base 85 Protrusion 90 Load transfer body 94 Hydraulic jack (hydraulic mechanism) 95,95a inner tube 98 Third cylinder 100 Cast-in-place concrete piles 110,110a outer tube 112 Second cylinder

Claims

1. A cast-in-place concrete pile with a circular cross section having an enlarged diameter portion at the middle and tip of the pile shaft, A concrete pile body having an intermediate expanded diameter portion in the middle of the pile shaft portion and an expanded bottom portion at the tip of the pile shaft portion; a cylindrical protrusion provided at the central lower end of the expanded bottom portion, A cast-in-place concrete pile, characterized in that the outer dimensions of the protrusion are equal to or smaller than the outer dimensions of the pile shaft.

2. 2. The cast-in-place concrete pile according to claim 1, wherein the lower limit of the outer dimension of the protrusion is the outer diameter of a small-diameter pile hole for the pile shaft that is created as a guide hole for the pile shaft.

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