JP4542888B2 - Steel pipe pile - Google Patents

Description

  This invention is a steel pipe pile that is used as a foundation pile for building structures and civil structures, and is buried in the ground by rotational force and pressing force, and has a mechanism for excavating the ground, increasing the tip support force of the pile Therefore, the present invention relates to a rotary press-fit bottomed steel pipe pile having a tip part whose diameter is larger than the outer diameter of the steel pipe pile at or near the tip part of the pile.

  In conventional rotary press-fit bottom expanded steel pipe piles, a spiral blade is fixed by winding almost along the outer periphery of the pile tip, and a notch is provided in a part of the spiral blade to discharge gravel and cobblestone upward. The action of the excavation claw that makes it easy to do and attaches a blade piece of a predetermined width to a predetermined position on the outer periphery corresponding to the notch to compensate for the decrease in the supporting force due to the notch and softens the soil at the tip of the pile There are some which are devised so that a bit piece for projecting and projecting the steel pipe pile into the ground smoothly can be constructed (Japanese Patent Laid-Open No. 2003-64671, hereinafter referred to as Prior Art 1).

  In addition, a flange-shaped widened plate is formed on the outer periphery of the lower end of the tip of the pile, and at least one notch portion is provided in a part of the widened plate, and a lower blade and an upper blade are attached to the cutout portion. A drilling blade composed of a blade that is convexly curved in the direction of normal rotation in plan view is provided at the tip of the pile so that the earth and sand are discharged and the cutting soil is pressed and pressed around the sides of the steel pipe pile. (Japanese Patent Laid-Open No. 2003-27475).

During pile construction, the ground is excavated with the lower blade and excavating blade, and the excavated earth and sand passes through the notch and is discharged by the upper blade above and to the side of the bottom expansion plate for low vibration, low noise, and no waste. After being constructed in the ground with soil, and after construction, a device has been devised to give a large tip support force to the pile by means of a bottom plate (hereinafter referred to as Conventional Technology 2).
JP 2003-64671 A JP 2003-27475 A

  However, the above-described technique has advantages, but has the following problems.

1) The first problem The vertical bearing capacity of the pile is the allowable bearing capacity determined by the pile material (the strength of the pile material) and the allowable bearing capacity determined by the ground (the vertical bearing capacity determined by the ground of the pile is the circumferential frictional force. In this case, the smaller value is adopted, but generally the allowable bearing force determined by the ground is smaller, so the ground level is the same as the vertical bearing force determined by the pile material. It can be said that when the vertical bearing force determined by is increased, the bearing capacity performance of the pile is the largest and economical.

  Therefore, the rotary press-in bottom expanded steel pipe pile described in the background art increases the bottom end support force (the front end support force is directly proportional to the effective area of the pile front end portion subjected to the ground reaction force). The described rotary press-fitted bottom expanded steel pipe pile is provided with a spiral blade or a bottom expansion plate near the tip of the pile body to form a bottom expansion portion (hereinafter referred to as a bottom expansion portion). It has been devised to increase the effective area of the tip of the pile by having both the area and the bottom area of the expanded bottom.

  However, if the overhang of the expanded bottom portion from the pile body is increased, the resistance force acting on the pile is increased.

  For example, at the time of construction, piles are buried by the rotational force and pressing force of the construction machine, but a hard ground such as a gravel layer or a consolidated clay layer (the hard ground here is a ground having an N value of 30 or more. The N value is an index indicating the hardness of the ground, meaning that the higher the numerical value, the harder it is, and the value obtained by a standard penetration test, which is a kind of ground survey. When penetrating a pile, the ground reaction force acts on the expanded base due to the pressing force, and a large bending moment acts on the pile body and the expanded base.When the pile is shared, the ground reaction force acts on the expanded base due to the pile load, etc. The moment acts on the pile body and the expanded bottom.

  Therefore, in order to have the strength that the expanded base part does not deform at the time of construction or after sharing, and to increase the tip support force, the thickness or material strength of the pile body is increased, and the plate thickness or material strength of the expanded base part is increased. Therefore, the material cost is increased, the manufacturing is not easy, and the manufacturing cost of the pile is increased, which is uneconomical.

2) The second problem The rotary press-in bottom expanded steel pipe pile described in the background art is provided with a bottom expanded portion at the tip of the pile body, and by expanding the bottom area of the pile tip, The purpose is to increase the ground contact area and increase the tip support force of the pile.

  However, as disclosed in Japanese Patent Application Laid-Open No. 10-219682, some anti-main body tip portions are open. For this reason, the pile body has a pile diameter larger than a predetermined pile diameter, and a blocking effect cannot be obtained. Compared with steel pipe piles where the pile tip is closed, the effective area for the ground reaction force at the pile tip is smaller and the pile tip support is smaller and less expensive than when the pile tip is closed. there were.

3) Third problem The rotary press-in expansion bottom steel pipe pile described in the background art applies rotational force and pressing force to the pile body with construction machinery, and excavates the ground with spiral blades and excavation blades formed at the tip of the pile. The excavated soil is discharged upward from the notch, and the underground is excavated.When the pile is rotated on a hard intermediate layer or support layer such as gravel or hard clay, A large reaction force works in the direction opposite to the direction of excavation rotation.

  A steel pipe pile like the prior art 1 is provided with a cutout portion formed by fixing a spiral blade or a wing almost once around the outer periphery of the tip of the pile (for example, Patent Document 1), Since the excavation part and the sediment discharge part are one place, the large reaction force acting in the opposite direction to the excavation rotation direction acts on the pile tip as an eccentric force from the pile central axis, and the vertical direction This may reduce the vertical workability of the pile and reduce the bearing capacity performance of the pile when shared.

  Furthermore, as the tip depth of the pile becomes deeper and the ratio of the pile length to the pile diameter increases, the rotation between the rotation axis of the pile tip and the rotation axis of the pile body will occur, and the pile body will continue to rotate while being curved. The alternating force of compression and tension acting on the curved part of the body has problems such as degrading the strength of the pile body and damaging the pile body.

4) Fourth problem The rotary press-in expansion bottom steel pipe pile described in the background art is a support pile that is rotary-inserted and buried in the ground, and the tip support force of the pile is that of the support layer ground near the tip of the pile. Since it increases in proportion to the hardness, the construction cost is more economical if the tip of the pile is penetrated into a hard ground with a predetermined layer thickness to increase the supporting force per one piece.

  However, when the pile is penetrated into the hard ground, it is difficult to consolidate the excavated sediment to the side of the tip of the pile, and in order to advance the pile, the excavated sediment is discharged and moved from the tip of the pile. It will be necessary.

  Therefore, the steel pipe pile of the prior art 1 is attached by inclining the earth and sand on the bottom surface of the bottom expanded portion formed by the spiral blade fixed substantially by winding around the outer periphery of the pile tip in the axial direction of the pile body. The spiral pipe and excavation blades are used for excavation, and the excavated soil is devised to move through the notch and above the expanded bottom. The conventional steel pipe pile is formed with a flange-shaped expanded plate on the outer periphery of the lower end of the steel pipe pile. The bottom surface of the expanded bottom portion is excavated with a lower blade attached to the expanded bottom plate, and the excavated earth and sand is moved above the expanded bottom plate with the upper blade attached to the expanded bottom plate through the notch. Has been made.

  However, since the steel pipe pile of the prior art 1 is attached in the same vertical direction (not inclined) as the axial direction of the pile body, the bit piece attached to the bottom bottom portion of the pile body tip portion has no sliding surface of excavated earth and sand. The excavated earth and sand on the lower surface of the tip of the pile body is difficult to discharge and move upward from the tip of the pile.

  The steel pipe pile of prior art 2 is consolidated in the same vertical direction (not inclined) as the axial direction of the pile body, although the excavated earth and sand is consolidated to the side of the pile tip part by the excavating blade attached to the bottom bottom of the pile body tip part. Since there is no sliding surface of the excavated earth and sand, there is no mechanism for discharging and moving the excavated earth and sand on the lower surface of the lower end of the pile body upward from the upper end of the pile.

  Therefore, the construction was difficult when the pile was penetrated into the hard intermediate layer or the hard support layer ground.

5) Fifth problem Since the rotary press-in expanded steel pipe pile described in the background art forms a bottom expanded part by directly attaching a spiral blade and a bottom expanded plate near the tip of the pile, the pile main body and the pile front end are integrated. When the piles were transported, the bottoms were bulky and the transportation costs were uneconomical.

  The present invention has been made in view of the above problems, and a mechanism for reducing the influence of a large bending moment acting on a pile body by a ground reaction force acting on a bottom expanded portion having a diameter larger than the outer diameter of the pile body. It has an excavation mechanism that can penetrate into a hard intermediate layer or a hard support layer ground without deformation of the pile tip even during construction or sharing even in hard ground with an N value of 50 or more in the standard penetration test, A steel pipe pile that increases the support capacity of the tip of the pile by increasing the effective area against the ground reaction force at the tip of the pile, and is further divided into the pile body and the tip of the pile so that the bottom of the pile does not become bulky when the pile is transported An object of the present invention is to provide a rotary press-fitted bottom-pipe steel pipe pile that has a large pile support capability, has good workability, is economical, and has low transportation costs.

In order to solve the above-mentioned problem, the first invention is a steel pipe pile embedded in the ground by a rotational force and a pressing force, and has an expanded bottom for increasing the supporting force of the pile at the tip of the pile. A connecting short pipe having a plate, a drilling blade of a cutout portion of the bottom plate, and a tip drilling blade ,
Two or more notches on the bottom plate are provided at approximately the same interval from each other,
The excavating blade has a shape equivalent to a shape obtained by dividing an elliptical double-circular plate material into four parts by an elliptical minor axis centerline and an elliptical major axis centerline, and is cut in a notch portion of the expanded base plate. Inclined so as to scoop up earth and sand, the inner diameter part of the double circle is connected along the outer surface of the short pipe for connection,
The tip excavation blade is a plate-shaped excavation blade fixed downward with respect to the bottom surface center of the bottom expansion plate,
The plate-shaped excavating blade has a line connecting the center point of the lower side of the plate shape and the apex of the left and right upper side corners as a folding line, and each lower side corner is bent in the normal rotation direction of the pile to The steel pipe pile is characterized by being formed so as to transfer excavated earth and sand near the bottom center of the bottom plate to the excavating blades of the bottom plate by rotation of the pile.

Moreover, 2nd invention is a steel pipe pile characterized by fitting and fixing the said short pipe for a connection and a steel pipe pile main body on-site.

  According to 1st invention, since the short pipe for pile connection which has a larger diameter than the outer diameter of a pile main body was provided in the junction part of a pile main body and a bottom expanded board, the ground which acts on a bottom expanded board at the time of construction of a pile or after common use The influence of the large bending moment due to the reaction force is reduced, and the bending moment acts on the pile connecting short pipe, and therefore does not act directly on the pile body.

  Therefore, it is economical because it is not necessary to make the thickness and strength of the pile main body or the plate thickness and strength of the pile expanded bottom plate larger than necessary.

  According to 2nd invention, since the notch part and excavation wing | blade of a pile expanded bottom part are provided in multiple places, and the excavation part of a ground and the discharge part of earth and sand are multiple places, it is with respect to a pile front-end | tip part at the time of construction The eccentric force from the working pile central axis is greatly reduced, improving the vertical workability of the pile in the vertical direction, and improving the bearing capacity performance of the pile when shared.

  In addition, the vertical workability of the pile is improved, so that the rotation axis of the pile and the rotation axis of the pile body are displaced, and the pile body continues to rotate while it is curved, and the compression and tension acting on the curved part of the pile body The alternating force reduces the strength of the pile body and reduces the effect of damaging the pile body.

  According to the third invention, the excavation blade is fixed to the bottom expansion plate and the short pipe for connecting the pile by welding or the like to serve as a reinforcing material for the bottom expansion plate, and works on the bottom expansion plate at the time of construction or after sharing the pile. The influence of the large bending moment exerted by the ground reaction force is reduced to prevent the deformation of the bottom plate, and at the time of pile construction, the tip of the excavation blade excavates the ground on the bottom surface of the excavation plate, and the excavated soil covers the upper surface of the excavation blade. Drilling performance on hard ground by sliding upward from the anti-tip (when excavating hard ground, the excavated sediment cannot be consolidated into the pile measurement, and the excavated sediment is moved upward from the tip of the pile. Need to be moved to).

  Furthermore, the excavation angle with respect to the ground can be easily changed according to the type of excavated ground, and the workability of the pile is enhanced (inclined with respect to the axial direction of the pile connecting short pipe and inclined toward the reverse rotation direction side of the pile) If the angle of the excavating blade is increased, the excavation performance increases, and if the excavation angle is decreased, the construction speed increases.)

  In addition, the shape of the excavating blade is not bent and is easy to manufacture and economical.

  According to the fourth invention, the excavated earth and sand at the tip of the pile main body excavated by the tip excavating blade provided with the excavating claw having a lifting function slides on the surface of the excavated claw by the normal rotation at the time of burying the pile, and the pile is expanded The excavation performance for the hard ground is improved because it passes through the notch provided in the part and is discharged above the pile body. (When excavating hard ground, the excavated soil cannot be consolidated to the side of the pile. It is necessary to move the excavated earth and sand above the tip of the pile.)

  In addition, the tip excavation blade, which is a plate excavation blade that is bent downward in the forward rotation direction of the pile and that protrudes while tilting and is fixed downward with respect to the center of the bottom surface of the bottom expansion plate, has a simple structure. Manufacture is easy, leading to a reduction in manufacturing costs.

  According to the fifth aspect of the invention, the pile tip portion formed by providing the pile bottom plate, the excavation blade, and the tip excavation blade on the pile connecting short pipe has an inner diameter substantially equal to the outer diameter of the pile body. Since the short pipe for connection can be fixed by inserting it into the tip of the pile body, if the pile tip and the pile body are divided during transportation, there is no bulkiness, low transportation cost, and easy handling It is. Can be fixed on the site by welding.

  Furthermore, the corrosion rate of steel pipes (corrosion rate of steel pipes handled in the construction field is generally 1 mm in 50 years, but in the ground such as acid clay and seawater reclaimed land, the corrosion rate of steel pipes is increased. To increase the resistance of the steel pipe pile against the horizontal stress among the stresses acting on the pile, so that the pile material strength of the pile body is increased. If necessary, it can be dealt with by changing the thickness of the pile body without changing the structure and shape of the pile connecting short pipe at the tip, while maintaining the outer diameter of the pile body.

  One embodiment of the present invention is shown in FIG. 1, FIG. 2, FIG. 3, and FIG.

  1 is a front view (1), a plan view (2), and a bottom view (3) of a rotary press-fitted bottom expanded steel pipe pile, FIG. 2 is a perspective view of a bottom expanded plate, and FIG. 3 is a plan view of a drilling blade. FIG. 4 is a perspective view of the tip excavation blade.

  As shown in FIG. 1, the rotary press-fit expanded bottom steel pipe pile 1 of the present embodiment is composed of a pile body 2 and a pile front end, and the pile front end includes a pile connecting short pipe 3, a bottom expanded plate 4, a drilling blade. 5 and a tip excavating blade 6.

  The pile body 2 and the pile connecting short pipe 3 in the present embodiment are formed of a steel pipe having a predetermined length, outer diameter, and thickness (if collapsed, a structural carbon steel pipe), but in this embodiment The pile body 2 is made of a material STK400 having an outer diameter of 190.7 mm and a wall thickness of 5.3 mm. The pile connecting short pipe 3 is made of an outer diameter of 216.3 mm, a wall thickness of 12.7 mm, and a length of 100 mm. It is assumed that STK400 is used.

  The bottom expansion plate 4, the excavation blade 5, and the tip excavation blade 6 are formed of a steel plate having a predetermined plate thickness.

  The expanded bottom plate 4 is formed in a circular shape with an outer diameter (Φ3) that is about twice the outer diameter (Φ1) of the pile body 2, but in this embodiment, the outer diameter (Φ3) of the expanded bottom plate 4 is 370 mm, The thickness was set to 32 mm and the material SS400.

  Two or more cutouts 4A are formed at a point-symmetrical position from the center point M of the bottom expansion plate 4 formed in a circle or at the same center angle. In this embodiment, a phase of 180 degrees is formed. Then, two notches 4A are formed.

  As shown in FIG. 2, the cutout portion 4A has a line segment L1 on the circle centerline 4A1 and a position obtained by translating the centerline 4A1 by a predetermined distance W in the reverse rotation direction of the pile. A portion surrounded by a certain line segment L2 and an arc L3 in contact with the outer periphery of the pile connecting short pipe 3 is cut and formed by a predetermined method.

  The shape of the pile connecting short pipe 3 is a hollow cylindrical body of a predetermined height, the bottom and top surfaces of the hollow cylindrical body and the central axis are formed vertically, the inner diameter of the pile main body 2 is fitted, and the pile It has substantially the same size as the outer diameter (Φ1) of the main body 2, and has an outer diameter (Φ2) larger than the outer diameter (Φ1) of the pile main body 2.

  A predetermined method is employed in such a manner that the bottom surface of the pile connection short pipe 3 is disposed on the top surface of the bottom expansion plate 4 in which the notch 4A is formed, and the center axis of the short tube 3 for pile connection passes through the center point M of the bottom expansion plate 4. (For example, welding) and fix.

  The shape of the excavating blade 5 in plan view is shown in FIG. The shape of the excavating blade 5 shown in FIG. 3 in plan view is substantially the same as a shape obtained by dividing a ring-shaped elliptical double circle into four parts by the centerline of the elliptical minor axis and the centerline of the elliptical major axis. The inner diameter SL1 of the elliptical short-diameter side excavating blade having the same shape is substantially equal to the outer diameter (Φ2) of the pile connecting short pipe 3 shown in FIG. 1, and the elliptical long-diameter side excavating blade inner diameter LL1 is predetermined. Is the length of

  The excavation blade 5 is inclined from the axial direction of the pile connecting short pipe 3 at each of the notch portions 4A provided in a plurality of locations on the pile widening plate 4, and is connected to the pile widening plate 4 and the pile connecting short pipe 3. Although fixed by a predetermined method (for example, welding), the tip end portion of the excavation blade 5 and the line segment L2 of the cutout portion 4A are substantially overlapped with each other when viewed from the upper surface of the bottom expansion plate 4, and the rear surface of the excavation blade 5 The part is fixed to the line segment L1 of the notch 4A.

  The attachment angle of the excavation blade 5 can be adjusted with respect to the axial direction of the pile connecting short pipe 3 by adjusting the length of the inner diameter of the excavation blade on the elliptical long diameter side.

  As shown in FIG. 4, the tip excavation blade 6 forms excavation claws 7 by bending lower corners of a steel plate having a predetermined plate thickness in a quadrilateral plan view in the normal rotation direction P of the pile. The folding line 7 is substantially equal to the midpoint of the lower side of the quadrilateral in the vertical direction and the line segments passing through the upper corners.

  The upper side of the tip excavating blade 6 is fixed (for example, welded) to the lower surface of the bottom expansion plate 4 by a predetermined method (see FIG. 1 (3)). It is good to fix to the center line which passes along the center side corner | angular part (CC) of the cutting line of the reverse rotation direction of the pile of each notch part 4A formed in to substantially the same position.

"Effect of the embodiment"
According to this embodiment, the first effect of the embodiment is that a supporting pile is large, easy to manufacture, and an inexpensive pile can be obtained.

  As the support force of the pile, a smaller value is adopted among the allowable support force determined by the pile material and the allowable support force determined by the ground, but generally the allowable support force determined by the ground is smaller.

  For example, in the case of a steel pipe having an outer diameter of 190.7 mm, a wall thickness of 5.3 mm, and a material STK400 set in the present embodiment, the long-term allowable support force (allowable support force is determined by the pile material of the pile main body 2 is There is a short-term allowable bearing capacity that is considered by adding a load that increases in the event of an earthquake to the load of the structure, and a long-term allowable bearing capacity that considers only the load of the structure at normal times. When the long-term allowable bearing capacity of the pile satisfies the waiting force, generally the short-term allowable bearing capacity of the pile satisfies the short-term allowable bearing capacity required for design. ) Is 360 kN, but the long-term allowable bearing force determined by the ground when the pile body 2 itself is buried as a pile is not based on this embodiment, but the N value of the support layer ground is 50 (N value is a numerical value representing the hardness of the ground. In the case of the construction field, a maximum of 50 is generally adopted in the construction field, but the tip bearing force is approximately 95.1 kN. The long-term allowable bearing force is 95.1 kN. (The calculation formula used was 200 × N value of ground at the tip of the pile × Effective bottom area of the tip of the pile / 3.)

  However, according to the present embodiment, the pile tip 2 is formed on the pile body 2, and the outer diameter of the bottom expansion plate 4 is set to 370 mm. Therefore, when the N value of the support layer ground is 50, long-term allowable support determined by the ground Since the force is approximately 358.2 kN, the maximum long-term allowable bearing force of the pile in this case is 358.2 kN, and the long-term allowable bearing force of the pile increases 3.76 times.

  As a result, the number of piles used is greatly reduced, so the construction cost is greatly reduced due to the reduction of material costs and the shortening of construction days, which is economical.

  Furthermore, the outer diameter of the pile connecting short pipe 3 provided on the bottom expansion plate 4 is larger than the outer diameter of the pile main body 2, so that the overhang of the bottom expansion plate 4 is reduced. Since it is being fixed to the outer peripheral part of the short pipe 3 for pile connection, the influence of the moment of the ground reaction force which works the role of a reinforcement rib and acts on a pile front-end | tip part is reduced significantly with respect to the pile main body 2. FIG.

  For this reason, the board thickness of the bottom expansion board 4 can be made thin. For example, regardless of the present embodiment, when the pile is configured by directly fixing the bottom expansion plate 4 to the pile body 2 without providing the pile connecting short pipe 3, the long-term allowable bearing force of 358.2kN is provided at the tip of the pile. Load (the maximum long-term allowable bearing force determined by the ground is 358.2 kN when the outer diameter of the expanded base plate 4 set in the embodiment is 370 mm) is applied, the expanded base 4 and the pile body 2 In order not to be deformed, the thickness of the bottom expansion plate 4 needs to be considerably increased, the material cost increases, the processing is difficult, and the production cost increases.

  However, according to this embodiment, the standard of the pile connecting short pipe 3 is set to an outer diameter of 216.3 mm, an inner diameter of 12.7 mm, and a material STK400, and the standard of the excavating blade 5 is set to a plate thickness of 24 mm and a material STK400. When the load of 358.2 kN of long-term allowable bearing force is applied to the pile tip, if the plate thickness of the bottom expansion plate 4 is set to about 32 mm for the material SS400 and about 24 mm for the material SS540, the tip of the pile Has been confirmed not to deform.

  However, material costs are reduced, processing is easy, and production costs are drastically reduced.

  The second effect of this embodiment is that the workability of the pile is improved.

  Since the notch 4A formed on the bottom expansion plate 4 and the excavation blade 5 fixed in the vicinity thereof are provided at two positions with a phase of 180 degrees, the eccentric force applied to the pile main body at the time of rotary embedding is reduced, and the pile The excavating earth and sand at the tip of the pile body excavated by the excavating blade 6 provided on the lower surface of the bottom expansion plate 4 is improved in the vertical workability. Is moved upward and outward from the center axis of the pile, moved to the vicinity of the notch 4A, and is excavated and discharged above the expanded plate 4 by the excavating blades 5 provided on the expanded plate 4. It can be easily penetrated even on a hard ground having a high N value of 50 or more.

  A third effect of the present embodiment is that transportation costs are reduced.

  In this embodiment, since the pile main body 2 has a structure that is fitted into the pile connection short pipe 3 and fixed to the pile tip portion, only the pile tip portion is manufactured at the factory, and the pile main body 2 and the pile are constructed at the construction site. If the tip portion is fixed by a method such as welding, the pile tip portion and the pile body 1 can be transported separately, and the transportation cost is reduced without being bulky.

  Furthermore, in this embodiment, since the pile main body 2 uses the structural carbon steel pipe of the standard generally sold, it can be easily obtained in various parts of the country, and the construction site spans the prefecture, etc. In such a case, the pile body 2 can be procured locally by transporting only the pile tip.

It is the side view, top view, and bottom view which show the Example of the steel pipe pile of this invention. It is a perspective view which shows the Example of the bottom expansion board of the steel pipe pile of this invention. It is a top view which shows the Example of the excavation wing | blade of the steel pipe pile of this invention. It is a perspective view which shows the Example of the tip excavation blade of the steel pipe pile of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotating press fit bottom steel pipe pile 2 Pile main body 3 Pile connection short pipe 4 Bottom plate 5 Drilling blade 6 Tip drilling blade 7 Drilling claw

Claims (2)

A steel pipe pile buried in the ground by a rotational force and a pressing force, and at the tip of the pile, a bottom expansion plate for increasing the supporting force of the pile, and a drilling blade of a notch portion of the bottom expansion plate, A connecting short pipe having a tip excavating blade is provided ,
Two or more notches on the bottom plate are provided at approximately the same interval from each other,
The excavating blade has a shape equivalent to a shape obtained by dividing an elliptical double-circular plate material into four parts by an elliptical minor axis centerline and an elliptical major axis centerline, and is cut in a notch portion of the expanded base plate. Inclined so as to scoop up earth and sand, the inner diameter part of the double circle is connected along the outer surface of the short pipe for connection,
The tip excavation blade is a plate-shaped excavation blade fixed downward with respect to the bottom surface center of the bottom expansion plate,
The plate-shaped excavating blade has a line connecting the center point of the lower side of the plate shape and the apex of the left and right upper side corners as a folding line, and each lower side corner is bent in the normal rotation direction of the pile to A steel pipe pile which is formed and is provided so as to transfer excavated earth and sand near the bottom center of the bottom plate to the excavation blades of the bottom plate by rotation of the pile. The steel pipe pile according to claim 1 , wherein the short pipe for connection and the steel pipe pile main body are fitted and fixed on site.

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