JP2022171498A - Diameter-enlarged excavation structure in ground excavation head for forming sheet pile installation hole, and excavation head comprising the same - Google Patents

Abstract

To provide a diameter-enlarged excavation structure capable of preventing reaction force load in diameter-enlarged excavation from becoming excessive and suppressing reduction in an original excavation efficiency and risk of damage and early wear in order to perform diameter-enlarged excavation suitable for pile installation requiring a wide diameter-enlarged area and ground excavation requiring reasonable diameter-enlarged excavation capacity such as hard bedrock.SOLUTION: A diameter-enlarged excavation structure comprises: a support frame (21) provided in the middle of a blade passage of each spiral blade (3) around a rod shaft (100); a movable arm (1) rotatably supported by each support frame; and a bit set (5) comprising a plurality of conical bits (51, 52) arranged in parallel on one side face of a tip of each movable arm. Since a rotary axis (RA) of a support shaft (22) is set to be sloped by an obliquely upward slope angle (2Rθ) with respect to a rod axis (CA), the movable arm and the bit set in a storage state (S2) are stored in an upper part of the spiral blade.SELECTED DRAWING: Figure 2

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diameter expanding structure for excavating and forming an enlarged diameter portion larger than the head diameter in a sheet pile driving hole forming head for driving sheet piles, and an excavating head provided with the same.

Conventionally, the structure described in the following document is disclosed as a structure in which a hammer head with spiral blades for driving sheet piles is provided with a movable arm.

Patent Document 1 (Japanese Patent Application Laid-Open No. 2020-197001) discloses a structure in which a U-shaped holder 23 is integrated near the outer periphery of a cutting tool 16, and a rod-shaped enlarged diameter claw 22 is accommodated therein. disclosed.

In Patent Document 2 (No. 3110253), a pivot metal fitting is provided by cutting out a spiral plate, and a base end of an enlarged bit 23 is inserted between both parallel piece portions 25, 25 of the pivot metal fitting. A structure is disclosed in which the expansion bit 23 is horizontally rotatably supported around the pivot 27 by penetrating the parallel pieces 25 and 25 and the expansion bit 23 with the pivot 27 vertically.

In Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2004-332253), double helical screws 21, 21 are formed on the outer periphery of a drilling bit body 33, and a plurality of drilling tools are fixed to the outer periphery of the tip of the drilling bit body 33. Claws 22, 22 . . . are fixed. Further, enlarged wings 23, 23 are rotatably supported by pins 24, 24 at predetermined positions of the screws 21, 21, and the enlarged wings 23, 23 are arranged so that the drilling bit body 33 faces the drilling direction. A structure is disclosed that is configured to be closed and in a stowed position when rotated clockwise, and to be expanded and ready for excavation when rotated counterclockwise.

Japanese Patent Application Laid-Open No. 2020-197001 Tomi No. 3110253 JP-A-204-332253

However, both the drilling head and the drilling bit are equipped with a relatively small diameter-expanding pawl or expanding blade that can be accommodated on the lower surface side of the helical blade. Small claws and wings have a limited diameter expansion area, and are not suitable for pile driving that requires a relatively wide diameter expansion area, such as hat-type sheet piles, and ground excavation that requires a corresponding expansion excavation capacity, such as hard rock. .

Here, in order to secure the diameter expansion distance of the diameter expansion claws and the diameter expansion blades, it is conceivable to increase the size of the claw portions and the wing pieces themselves. However, simply increasing or increasing the dimensions of the conventional diameter-expansion claws and expansion wings results in an excessive reaction load during diameter-expansion excavation. It can reduce the natural drilling efficiency and increase the risk of damage and premature wear.

In addition, simply lengthening or enlarging the dimensions of the conventional diameter-enlarging claws and enlarging blades interferes with surrounding cutting tools and screws, restricting the turning angle during storage. In addition, a portion of the diameter-expanding claw or the expanding wing protrudes outward, making it impossible to store in a compact manner, making it difficult to collect the excavating head after excavation or placement.

Therefore, in the present invention, in order to perform diameter expansion excavation suitable for pile driving that requires a relatively wide diameter expansion area such as a hat-type sheet pile and ground excavation that requires a suitable diameter expansion excavation ability such as hard rock,
To provide a diameter-expansion excavation structure capable of preventing an excessive burden of reaction force during diameter-expansion excavation and suppressing the risk of lowering of original excavation efficiency, damage and early wear.

Another object of the present invention is to provide a diameter-expansion excavation structure that can be stored in a compact storage form while ensuring a relatively large diameter-expansion area.

In order to solve the above problems, the following configuration is provided.

[1] (Upper storage by tilting the support shaft and ensuring excavation capacity by installing conical bits side by side)
The diameter expansion excavation structure in the ground excavation head for forming the sheet pile driving hole of the present invention is
A ground excavating head having a plurality of spiral blades (3 (3A, 3B, 3C)) around a rod axis (100),
a support frame (21) having a support shaft (22) with a specific angle provided in the middle of the blade path of each spiral blade (3);
a movable arm (1) rotatably supported around a support shaft by each support frame;
a bit set (5) consisting of a close group of a plurality of conical bits (51, 52) detachably arranged side by side on one side of the tip of each movable arm;
With the rod shaft (100) rotating in the forward rotation direction,
Each movable arm (1) rotates around one direction of the support shaft to a predetermined first regulation position (S1) by its own inertia, and the bit set at the tip of the arm is positioned outward from the outer shape of the spiral blade in the axial plane view. While it becomes a diameter expanded state (Fig. 3) protruding to
With the rod shaft (100) rotating in the reverse rotation direction opposite to the forward rotation direction,
Each movable arm (1) rotates around the support shaft in the other direction by its own inertia to a predetermined second regulation position (S2), and the bit set at the tip of the arm moves inward from the outer shape of the spiral blade in the axial plane view. It will be in the housed state (Fig. 4),
The rotation axis (RA) of the support shaft (22) is inclined at a certain inclination angle (2Rθ) obliquely upward with respect to the rod axis (CA), so that the housing state (S2) is achieved. A movable arm and bit set are housed on top of the helical blade (eg Figures 8, 13).
In addition, the rotating shaft (RA) of the support shaft (22) is inclined at a certain angle inclined upward toward the vertical direction with respect to the normal line (3N) of the spiral blade, so that the accommodation state (S2) is achieved. is housed on top of the helical blade (eg FIG. 14).

In other words, this configuration simultaneously employs a structure in which bit sets are arranged side by side at the tip of a relatively long arm and an inclined setting of the support shaft. The side-by-side structure of the conical bits ensures excavation capability and abrasion resistance in the expanded diameter area, while the tilted setting of the support shaft enables storage in the upper part of the blade in the stored state, ensuring a compact storage form. there is The inclination setting solves the problem that it tends to protrude when the bit is installed side by side.

[2] (Upper storage by setting the support frame space toward the upper side)
In the diameter expansion excavation structure in the ground excavation head for forming the sheet pile driving hole,
The movable arm 1 has a first extending portion 11 closer to the base portion that is supported by the rotation shaft of the support frame 21 and extends in the first extending direction, and a curved portion 12 that continues from the first extending portion 11 . Consists of second extending portions 13 and 14 closer to the tip that extend in two stretching directions,
The frame space of the support frame that pivotally supports the first extending portion is provided above the blade thickness center of the spiral blade,
By being provided facing the spiral traveling direction to the rod axis,
It is characterized in that the movable arm and bit set in the housed state (S2) are housed in the upper part of the spiral blade that continues to the lower part of the support frame.
For example, as shown in side views of FIG. 7 and FIG. 8 of Embodiment 1, or side views of FIG. 13 and FIG. Meanwhile, the support frame 21 is located above the blade axis SA ( It is interposed and fixed at a position shifted upward in each drawing.

[3]
The movable arm 1 has a first extending portion 11 closer to the base portion that is supported by the rotation shaft of the support frame 21 and extends in the first extending direction, and a curved portion 12 that continues from the first extending portion 11 . Consists of second extending portions 13 and 14 closer to the tip that extend in two stretching directions,
Among these, the second stretching direction is inclined at a constant angle with respect to the first stretching direction,
A bit set consisting of a plurality of bits is provided on one side surface of the second extending portion in a specific direction orthogonal to the second extending direction so as to face the bit axial direction obliquely downward when viewed from the tip of the second extending portion. characterized by
(The bit axis direction of the bit set is set at an acute angle (inclination angle in the range of 45 degrees +-10 degrees) with respect to the rotation axis of the support frame) Ground for forming sheet pile driving holes An expanding drilling structure at the drilling head.

[4]
The movable arm 1 has a first extending portion 11 closer to the base portion that is supported by the rotation shaft of the support frame 21 and extends in the first extending direction, and a curved portion 12 that continues from the first extending portion 11 . It is composed of second extending portions 13 and 14 closer to the tip portion extending in two extending directions, and a plurality of bits are attached in parallel to a specific mounting surface closer to one side of the second extending portions 13 and 14. There is
The back side surfaces of the second extension portions 13 and 14 opposite to the attachment surfaces to which the bits are attached are closer to the attachment surface than the back side surface of the first extension portions when viewed from above the rotation shaft. is shifted in a stepped manner to the offset position of .

[5]
The spiral blade has a three-blade structure in which three blades are provided at equal phase intervals around the rod axis CA,
A support frame having a frame space is provided at a predetermined axial position of the rod shaft in the middle of each spiral path of the three spiral blades, and the movable arm is pivoted by a rotating shaft passing through each frame space. By being supported
The bit set 5 attached to the tip of the movable arm in the diameter-expanded state is characterized by three sets projecting outward from the outer shape of the spiral blade in an axial view at equal intervals around the center of the rod axis.

[6]
Each bit set 5 consists of a pair of conical bits 51, 52, two of which are attached closely to each other at equal intervals along the extending direction of the arm. It is characterized by facing in a direction substantially parallel to the tangential direction, or in an outward inclined direction inclined to the outside in the rotational direction (from the radial direction) from the tangential direction.

[7]
Each bit set is composed of a first bit closer to the tip and a second bit closer to the base, and is characterized in that the bit diameter of the second bit is set larger than that of the first bit closer to the tip.

In the state where the movable arm is attached to the helical blade, the bit axial directions of the first bit and the second bit are inclined downward at different angles with respect to the vertical center axis (rod axis) of the drilling head. may be characterized.

Furthermore, the embodiment described later is characterized in that the rotation support shaft of the movable arm is inclined obliquely upward with respect to the normal line of the spiral blade, and the bit mounting shaft is inclined obliquely downward.

By taking the above means, the present invention
To provide a diameter-expanding excavation structure capable of preventing an excessive burden of reaction force during diameter-expanding excavation and suppressing the risk of lowering of original excavation efficiency, damage, and early wear.

In addition, there is provided a diameter-expansion excavation structure that can be stored in a compact storage form while securing a relatively large diameter-expansion area.

As a result, it has become possible to perform diameter-expanding excavation suitable for piling that requires a relatively wide diameter-expanding area, such as hat-type sheet piles, and ground excavation, such as hard rock, that requires a corresponding ability to excavate for diameter-expansion.

FIG. 2 is a front view of the excavating head according to the first embodiment of the present invention, in a diameter-expanded state (S1); The front view of the excavation head of Example 1 in the stored state (S2) α-α plane sectional view of FIG. 1 perpendicular to the rod axis β-β plane sectional view of FIG. 2 perpendicular to the rod axis AA partial enlarged view of Fig. 3 BB partial enlarged view of FIG. AA partial enlarged view of FIG. 3 seen from the side view of the support frame (the peripheral end view of the spiral blade) BB partial enlarged view of FIG. 4 seen from the side view of the support frame (the peripheral end view of the spiral blade) Fig. 2 is a cross-sectional plan view of the excavating head of Example 2 of the present invention at a position corresponding to α-α in the expanded state (S1); Planar cross-sectional view of the drilling head of Example 2 at a position corresponding to β-β in the stored state (S2) CC partial enlarged view of FIG. DD partial enlarged view of FIG. CC partial enlarged view of FIG. 9 seen from the side view of the support frame (the peripheral end view of the spiral blade) Partially enlarged view of DD in FIG. 10 seen from the side view of the support frame (the peripheral end view of the spiral blade)

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the invention will be described with reference to drawings shown as Embodiments 1 and 2. FIG.

[Basic configuration]
The diameter expansion excavation structure in the ground excavation head for forming a sheet pile driving hole according to the present invention is a structure attached to the ground excavation head, and is used when the sheet pile is press-fitted into the ground while excavating the ground. This diameter-enlarged excavation structure excavates a diameter-enlarged area larger than the original head excavation diameter of the excavation head.

In particular, when driving sheet piles having a relatively large effective width, such as hat-type sheet piles, the diameter expansion excavation structure of the present invention is preferably used in order to reduce the number of pilot holes excavated for construction. The diameter-expansion excavation structure of the present invention is also preferably used in excavation into hard rock and sheet pile press-in work.

(Hat type sheet pile)
In the hat-shaped steel pipe sheet pile, the flange plate cross section connected to both ends thereof is inclined at an angle larger than 90 degrees with respect to the web plate cross section, and the arm plate cross section connected to the tip of each flange plate is inclined from the web plate cross section. are also relatively distant from each other. The distance between the ends of the left and right arm plates, that is, the effective width, is rated at 900 mm, and because it has a larger cross section than conventional square sheet piles, it is characterized by the fact that fewer sheets can be used in the same length of construction.

In such a hat-shaped sheet pile, as shown in FIG. While excavating in a circle with a three-point pile driver set with an earth auger and a casing, the expanded area on the outer diameter side of the excavated circle of the earth auger is excavated to expand the diameter, and the sheet pile is inserted into the expanded area. must be pressed in.

However, since it is necessary to secure the length in the radial direction in such a diameter expansion area, conventional small diameter expansion plates and diameter expansion claws cannot be used. There was a problem that the hat-shaped sheet pile could not be press-fitted.

In order to solve this problem, the present invention provides a curved and twisted movable arm that is tilted and supported by a support frame that is tilted in the middle of the path of the spiral blade, and a plurality of bit rows that are attached close to one side of the tip of the movable arm. By adopting a diameter expansion excavation structure consisting of, it is possible to reliably excavate even in a relatively large diameter expansion area and even in hard rock. It has become possible.

(Ground excavation head)
The ground excavating head of the present invention has a structure having a plurality of spiral blades (3 (3A, 3B, 3C)) around the rod axis (100).
Diameter expansion comprising a support frame interposed along the outer shape of the spiral in each spiral path of the plurality of spiral blades (3 (3A, 3B, 3C)) and a movable arm pivotally supported by the support frame It has an excavated structure.

(Expansion excavation structure)
The diameter expansion excavation structure of the present invention has, as a basic configuration,
a support frame (21) having a support shaft (22) with a specific angle provided in the middle of the blade path of each spiral blade (3);
a movable arm (1) rotatably supported around a support shaft by each support frame;
a bit set (5) consisting of a plurality of conical bits (51, 52) in close proximity, removably arranged side by side on one side of the tip of each movable arm.

(Diameter expansion state (S1))
With the rod shaft (100) rotating in the forward rotation direction,
Each movable arm (1) rotates around one direction of the support shaft to a predetermined first regulation position by its own inertia, and the bit set at the tip of the arm protrudes outward from the outer shape of the spiral blade in the axial plane view. It will be in the expanded state (S1).

(Contained state (S2))
On the other hand, when the rod shaft (100) rotates in the reverse rotation direction opposite to the forward rotation direction,
Each movable arm (1) rotates around the other direction of the support shaft to a predetermined second regulation position by its own inertia, and the bit set at the tip of the arm is accommodated inside the outer shape of the spiral blade in an axial plan view. It will be in the accommodation state (S2).

By setting the rotation axis (RA) of the support shaft (22) at a constant angle inclined upward toward the vertical direction with respect to the normal line (3N) of the spiral blade,
The movable arm and bit set in the stowed state (S2) are stowed on top of the helical blade.
In other words, this configuration simultaneously employs a structure in which bit sets are arranged side by side at the tip of a relatively long arm and an inclined setting of the support shaft. The conical bit side-by-side structure ensures excavation capability and abrasion resistance in the expanded area, while the tilt setting of the support shaft enables storage in the upper part of the blade in the stored state.

[Support frame 2]
(Upper storage by setting the support frame space closer to the upper part)
In the diameter expansion excavation structure in the ground excavation head for forming the sheet pile driving hole,
The support frame is composed of a substantially U-shaped frame and has a frame opening in one direction.
A frame space of the support frame that pivotally supports the first extending portion of the movable arm is provided above the blade thickness center of the spiral blade.
As a result, the movable arm and bit set in the housed state (S2) are housed in the upper part of the spiral blade that continues to the lower part of the support frame.

[Movable arm 1]
The movable arm is pivotally supported by the rotation shaft of the support frame and extends in the first extending direction through a first extending portion 11 closer to the base portion and a curved portion 12 continuing from the first extending portion 11 in the second extending direction. Consists of second extension portions 13 and 14 closer to the tip that extend to
Among these, the second stretching direction is inclined at a constant angle with respect to the first stretching direction,
A bit set consisting of a plurality of bits is provided on one side surface of the second extending portion in a specific direction orthogonal to the second extending direction so as to face the bit axial direction obliquely downward when viewed from the tip of the second extending portion. characterized by
In addition, the back side of the second extending portions 13 and 14 to which the bit is attached, which is opposite to the mounting surface, is located closer to the mounting surface than the back side of the first extending portion when viewed from above the rotation shaft. It is set stepwise to the offset position on the side.
(The bit axis direction of the bit set is set at an acute angle (inclination angle in the range of 45 degrees +-10 degrees) with respect to the rotation axis of the support frame) Ground for forming sheet pile driving holes An expanding drilling structure at the drilling head.

[Bit set]
A plurality of bits are mounted in parallel on the mounting surfaces of the second extending portions 13 and 14 of the movable arm near a specific side.
Each bit set consists of a series of two bits that are attached close to each other at equal intervals, and the bit shaft in the expanded state is in a direction substantially parallel to the tangential direction of the spiral blade in plan view, or inward in the traveling direction. Facing the inclining direction inclined to.

[Spiral feather]
The spiral blade consists of a three-blade structure in which three blades are provided at equal phase intervals around the rod axis,
A support frame having a frame space is provided at a predetermined axial position of the rod shaft in the middle of each spiral path of the three spiral blades, and the movable arm is pivoted by a rotating shaft passing through each frame space. By being supported
Three bit sets attached to the distal end of the movable arm in the diameter-expanded state protrude outward from the outer shape of the spiral blade in an axial view at equal intervals around the center of the rod axis.

(Example 2)
Each bit set of Embodiment 2 consists of a first bit closer to the tip and a second bit closer to the base, and the bit diameter of the second bit is set smaller than that of the first bit closer to the tip. .

With the movable arm attached to the spiral blade, the axial direction of each bit of the first bit and the second bit is inclined downward at different angles with respect to the vertical central axis (rod axis) of the drilling head. and

The rotation support shaft of the movable arm is tilted obliquely upward with respect to the normal line of the helical blade, and the bit mounting shaft is tilted obliquely downward with respect to the axial direction of the rod.

[Patent Points]
1: A movable arm with a double bit can be stored on the spiral blade.
A movable arm is rotatably supported at a position above the thickness direction of the spiral blade (FIGS. 7, 8, 13 and 14). In addition, the rotation support shaft of the movable arm is tilted in a direction closer to the vertical than the normal to the spiral blade (FIG. 14). As a result, the spiral blade is compactly accommodated in the space above the upper surface of the blade without notching.

2: Like Example 1, the movable arm has a curved + twisted part,
The point where the bit faces obliquely downward (as seen from the front of the arm tip) (Fig. 7).
As a result, when stored, the blade can be stored compactly without protruding from the outer shape of the blade, and when the diameter is expanded, the bit shaft located vertically and obliquely downward can efficiently perform impact excavation.

3: As in Example 2, the extension axis of the movable arm is stepped (offset) (FIG. 11).
As a result, when stored, the blade can be compactly stored without protruding from the outer shape of the blade, and when the diameter is expanded, the drill can be efficiently struck and excavated in the obliquely downward direction of the bit.

The configuration of the embodiment particularly has the following features.
(Feature 1) The movable arm is provided with a plurality of conical bits in which two or three or more are aligned along the extending direction of the arm in substantially the same direction. pivoted. Each bit axis of the plurality of conical bits is oriented obliquely downward within a range of 40°±5° with respect to the rod axis. As a result, the diameter of the movable arm expands during normal rotation, and the multiple bits continuously excavate the hard rock, thereby reliably expanding the original excavation diameter of the hammer head.
(Feature 2) The pin rotation axis is inclined upward (upward when facing the direction of spiral movement to the tip of the bit shaft) with respect to the normal line of the spiral blade at a first angle of inclination, and the direction of spiral movement is greater than that of the bit axis. It tilts obliquely downward at a second tilt angle. Here, the first tilt angle is set larger than the second tilt angle. Further, the bit shaft is attached so as to be inclined downward with respect to the pin rotating shaft and also downward with respect to the rod shaft at an acute angle of inclination. As a result, while the arm is housed in the upper portion of the spiral blade, when the arm is expanded, the conical bit strikes obliquely downward, substantially parallel to the direction of spiral movement of the spiral blade, with an axial angle to the rod within approximately 45°±5°. .
(Feature 3) The first and second bits consist of a combination of same-diameter bits, or a combination of a small-diameter bit on the tip side and a large-diameter bit on the base side. The mounting surface of the bit mounting frame 14 is set so as to be stepwise shifted.
(Feature 4) The movable arm has a base end of a semi-disc and extends in the first extension direction. A second arm 13 extending in the extending direction is connected to the second arm 13 . This third arm is twisted at a predetermined twist angle with respect to the first arm. Further, in the second embodiment, the back portion of the third arm is set at an offset position shifted in the bending direction with respect to the back portion of the first arm. The third arm is integrally formed with a second bit mounting frame 14 closer to the base and a first bit mounting frame 14 closer to the tip.

(Action and effect of the structure of the embodiment)
In the diameter-expanding excavation structure of the embodiment, the movable arm is curved at a predetermined bending angle in the bending direction when viewed from the support axis side, and is twisted at a predetermined twisting angle in the twisting direction, and the support shaft is A compact storage state is ensured by inclining within the range of a predetermined inclination angle (15°±10°) in the vertical direction with respect to the normal line of the spiral blade.

In addition, a plurality of conical bits are exchangeably attached to a predetermined mounting surface at the bent tip of the arm, and the plurality of conical bits are arranged in close proximity to each other from the arm base side to the tip side to form a rod. By setting the inclination angle in a predetermined range (45°±10°) obliquely below the axis, even if the diameter expansion area is large in the radial direction, suitable diameter expansion excavation that does not lose to the ground. Ensures strength and durability.

Since wear parts are concentrated in the conical bit, by replacing only the conical bit that has worn out due to long-term use, it is possible to secure the durability of the drilling head with the diameter-expanding structure as a whole.

In particular, the bit set comprises a combination of a relatively small diameter conical bit on the tip end side and a relatively large diameter conical bit on the base end side, so that the excavation reaction force received by the bit on the tip end side is reduced. is relatively suppressed, the bit on the base end side secures the capacity for diameter expansion excavation on the inner diameter side, and both excavation efficiency and durability can be achieved.

In addition, without narrowing the distal end of the movable arm with respect to the proximal end, the extension axis is shifted (offset) toward the first rotation direction and curved to ensure rigidity and durability of the arm. Combined with the conical bit having a smaller diameter toward the tip side, it is possible to ensure compactness in the stored state.

Various modifications can be made to the present invention without departing from the gist of the invention. For example, it is possible to omit or extract a part of the structure, to make the partial structure into parts, to combine exchangeable structures, or to replace it with a known structure.

Rod axis (100)
movable arm (1)
First extension part (11)
curved portion (12)
Second extension part (13) (14)
Tilt angle (2Rθ)
support frame (21)
Lower frame piece (21B)
Upper frame piece (21T)
support shaft (22)
Spiral blade (3) (3A, 3B, 3C)
Spiral blade normal (3N)
First regulation position (diameter expansion state) (S1)
Second regulation position (accommodated state) (S2)
bit set (5)
Conical bit (51, 52)
Rod axis (CA)
Rotating axis (RA)
Accommodated state (S2)
Blade axis (SA)

Claims (6)

In a ground excavating head having a plurality of helical blades around a rod,
a support frame provided in the middle of the blade path of each spiral blade and having a support shaft with a specific angle;
a movable arm rotatably supported around a support shaft by each support frame;
A bit set arranged side by side on one side of the tip of each movable arm,
An expansion excavation structure comprising
With the rod rotating in the forward rotation direction,
Each movable arm rotates around one direction of the support shaft to a predetermined first regulation position by its own inertia, and a diameter-expanded state in which the bit set at the tip of the arm protrudes outward from the outer shape of the spiral blade in an axial plan view. while
With the rod rotated in the reverse rotation direction opposite to the forward rotation direction,
Each movable arm rotates around the other direction of the support shaft to a predetermined second regulating position by its own inertia, and the bit set at the tip of the arm is accommodated inside the outer shape of the spiral blade in an axial plan view. ,
The rotation axis angle of the support shaft is a constant inclination angle inclined upward in the vertical direction with respect to the normal line of the spiral blade,
A diameter expansion excavation structure in a ground excavation head for forming a hole for sheet pile driving, characterized in that a movable arm and a bit set in a housed state are housed in the upper part of a spiral blade continuing to the lower part of a support frame. The movable arm extends in the second extending direction via a first extending portion closer to the base portion and extending in the first extending direction while being supported by the rotating shaft of the support frame, and a curved portion connected from the first extending portion. and a second extension part near the tip,
By providing the frame space of the support frame that pivotally supports the first extension part above the center of the blade thickness of the spiral blade,
Expanding excavation in the ground excavation head for forming a hole for sheet pile driving according to claim 1, characterized in that the movable arm and bit set in the housed state are housed in the upper part of the spiral blade continuing to the lower part of the support frame. structure. The movable arm extends in the second extending direction via a first extending portion closer to the base portion and extending in the first extending direction while being supported by the rotating shaft of the support frame, and a curved portion connected from the first extending portion. and a second extension part near the tip,
Among these, the second stretching direction is inclined at a constant angle with respect to the first stretching direction,
A bit set consisting of a plurality of bits is provided on one side surface of the second extending portion in a specific direction orthogonal to the second extending direction so as to face the bit axial direction obliquely downward when viewed from the tip of the second extending portion. A diameter expanding excavation structure in a ground excavation head for forming a sheet pile driving hole according to claim 1 or 2, characterized by: The movable arm extends in the second extending direction via a first extending portion closer to the base portion and extending in the first extending direction while being supported by the rotating shaft of the support frame, and a curved portion connected from the first extending portion. and a second extending portion closer to the tip, and a plurality of bits are attached in parallel to a specific mounting surface closer to one side of the second extending portion,
The back side of the second extending portion opposite to the mounting surface, to which the bit is attached, is at an offset position closer to the mounting surface than the back side of the first extending portion when viewed from above the rotation shaft. 4. The diameter-enlarging excavation structure in a ground excavation head for forming a sheet pile driving hole according to claim 1, wherein the excavation structure is set in a stepped manner. The spiral blade has a three-blade structure in which three blades are provided at equal phase intervals around the rod axis,
A support frame having a frame space is provided at a predetermined axial position of the rod shaft in the middle of each spiral path of the three spiral blades, and the movable arm is pivoted by a rotating shaft passing through each frame space. By being supported
A claim characterized in that three sets of bits attached to the tip of the movable arm in a diameter-expanded state protrude outward from the outer shape of the spiral blade in an axial view at equal intervals around the center of the rod axis. 5. A diameter expansion excavation structure in a ground excavation head for forming a sheet pile driving hole according to any one of 1, 2, 3, or 4. a rod axis;
three spiral blades spirally attached around the rod axis;
Excavation equipped with a support frame, a support shaft, and a movable arm of the diameter-enlarging excavation structure according to any one of claims 1, 2, 3, and 4, which are attached midway along each spiral path of three spiral blades. a head for
A ground excavation head for forming a hole for driving a sheet pile, wherein the three support shafts are arranged such that their attachment positions in the axial direction of the rods are offset from each other.

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