JP7598638B2 - Pile joint structure - Google Patents

Description

The present invention relates to a joint structure for longitudinally connecting piles, such as steel pipe piles, which are driven into the ground during foundation work for buildings, etc.

To connect steel pipe piles, it is common to create a groove at the lower end of the upper pile, ensure a root gap between the upper end of the lower pile, and then weld the outer periphery.
This welding work requires advanced skills, is subject to the effects of weather, and requires ultrasonic testing for quality control.
In addition, a shortage of welders has become evident in recent years, and many mechanical joints have been devised and are being used to solve this problem.
These mechanical joints can be broadly divided into fitting types and screw types.

One example of a fitting joint for steel pipe piles is described in Patent Document 1. This joint structure involves fixing an inner joint pipe with a pin insertion hole to the inner peripheral surface of the end of one of the steel pipe piles to be joined so that the pin insertion hole protrudes from the pile end, fixing an outer joint pipe that is thicker than the steel pipe pile base material and has a pin insertion hole that matches the pin insertion hole of the inner joint pipe to the end of the other steel pipe pile, fitting the outer joint pipe onto the outer peripheral surface of the inner joint pipe to match the pin insertion holes of the inner joint pipe and the outer joint pipe, and inserting and fixing a fixing pin into the pin insertion hole, thereby firmly joining one steel pipe pile to the other steel pipe pile.

One example of a screw-type steel pipe pile is described in Patent Document 2. In this joint structure, a male threaded joint part formed in a tapered shape with a specific inclination angle is provided at the tip of one of the steel pipe piles to be joined, and a female threaded joint part is provided at the tip of the other steel pipe pile, and these male threaded joint part and female threaded joint part are fitted together to join them.

JP 2001-11850 A Japanese Patent Application Publication No. 08-060652

In these joint structures, when the internal and external joint pipe of Patent Document 1 and the female and male threaded joint portion of Patent Document 2 are fixed to the end of the steel pipe pile by welding, the work needs to be carried out in advance at a factory or the like, which is expensive.
In addition, in the case of a fitting method such as the joint structure described in Patent Document 1, a clearance is required between the fixing pin and the pin insertion hole, so in a construction method such as a rotary pile where forward and reverse rotation is repeated, the pin insertion hole is deformed into an elliptical shape by the repeated rotation. If the deformation progresses further, it is thought that the fixing pin may break.
On the other hand, in the case of the screw method as in the joint structure described in Patent Document 2, the taper is large and the screw is a special screw, so it is more expensive. Moreover, even if a large torque is generated during normal rotation, there is a problem that it easily comes off during reverse rotation, and it is not suitable for the rotary pile construction method in which normal and reverse rotation are repeated.

The present invention aims to provide a pile joint structure which has the high forward rotation torque transmission performance and the ability to prevent disengagement during reverse rotation required for rotary pile construction methods, and which can be removed in the event of construction problems.

The pile joint structure of the present invention is a pile joint structure in which the ends of two piles are connected to each other by a joint member, and the end of the pile is formed with a tapered male screw portion that gradually reduces in diameter toward the tip, a pile-side shoulder portion that forms an annular plane that extends along a direction perpendicular to the longitudinal direction of the pile at the base end side of the male screw portion, and an annular tip surface that extends along a direction perpendicular to the longitudinal direction of the pile at the tip of the pile,
The joint member is formed in a cylindrical shape, and at both ends thereof, a female threaded portion that screws into the male threaded portion of the pile, a joint member side shoulder portion that forms an annular plane along a direction substantially perpendicular to the longitudinal direction of the joint member at the base end side of the female threaded portion, and an annular tip surface that extends along a direction substantially perpendicular to the longitudinal direction of the joint member at the tip of the joint member,
When the male threaded portion and the female threaded portion are screwed together, the annular tip surface of the joint member abuts against the pile side shoulder portion in a pressing state, and the annular tip surface of the pile abuts against the joint member side shoulder portion in a pressing state.

In this pile joint structure, the pile and the joint member are joined by the tapered male screw portion and female screw portion, and at that time, the annular tip surface of the joint member abuts in a pressing state against the pile shoulder portion, and the annular tip surface of the pile abuts in a pressing state against the joint member shoulder portion. The pressing state becomes larger as the tightening force between the male screw portion and the female screw portion increases, and the frictional force of the abutting surface allows the pile and the joint member to be joined with a powerful torque. In addition, the pressing force generates prestress (compressive stress) along the longitudinal direction in the pile and the joint member, and a strong connection against tension can be maintained. These synergistic effects prevent the connection from coming off even in the rotary pile construction method in which forward and reverse rotation are repeated. Of course, since it is a screw connection, it can be removed when necessary, such as when an abnormality occurs. Therefore, it is possible to remove the removed joint member and reuse it when necessary in the future.
Furthermore, since no welding is required, costs can be reduced and on-site construction is also made easier.

In this pile joint structure, the pile side shoulder portion and the joint member side shoulder portion are formed with an inclination in a direction perpendicular to the longitudinal direction that reduces the angle with the tapered surface of the male thread portion or the female thread portion, and the annular tip surface of the joint member and the annular tip surface of the pile are preferably formed with an inclination to match the corresponding pile side shoulder portion and the annular tip surface.

When a tensile force acts on the pile, the threads remain engaged near the longitudinal center of the male and female threads, but a force acts in a direction that separates them from each other at both ends of the threads. By forming the abutment surface between the shoulder portion and the annular tip surface so that the angle with the tapered surface of the threads is reduced in a direction perpendicular to the longitudinal direction, the movement of the ends of the joint member and the pile toward each other can be prevented by the mutual contact of the inclined surfaces, and a strong connection can be maintained along the entire length of the threads.

In this pile joint structure, the contact surface between the annular tip surface of the joint member and the shoulder portion on the pile side may have a width dimension along the radial direction larger than the contact surface between the annular tip surface of the pile and the shoulder portion on the joint member side.

If the contact surface with the joint member shoulder is large, the joint member can be made thicker to increase its strength, and even when a tensile force is applied, it can hold the two piles firmly without spreading.

The pile connecting method of the present invention is a method for connecting two piles in such a manner that the ends of the piles are connected to each other by a coupling member, and the pile has at its end a tapered male thread portion that gradually reduces in diameter toward the tip, a pile-side shoulder portion that forms an annular plane extending along a direction substantially perpendicular to the longitudinal direction of the pile at the base end side of the male thread portion, and an annular tip surface that extends along a direction substantially perpendicular to the longitudinal direction of the pile at the tip of the pile,
The joint member is formed in a cylindrical shape, and at both ends thereof, a female screw portion that screws into the male screw portion of the pile, a joint member side shoulder portion that forms an annular plane along a direction substantially perpendicular to the longitudinal direction of the joint member at the base end side of the female screw portion, and an annular tip surface that extends along a direction substantially perpendicular to the longitudinal direction of the joint member at the tip of the joint member,
When connecting the pile and the joint member,
The male threaded portion of the pile and the female threaded portion of the coupling member are screwed together, and the annular tip surface of the coupling member and the pile side shoulder portion, or the annular tip surface of the pile and the coupling member side shoulder portion are sequentially or simultaneously brought into pressure contact with each other, and then further tightened in that contact state.

The joint member of the present invention is a joint member for connecting two piles by joining male threads formed on the ends of the two piles, and is formed in a cylindrical shape, with a female thread portion at each end that screws into the male thread portion of the pile, a joint member side shoulder portion that forms an annular flat surface along a direction approximately perpendicular to the longitudinal direction at the base end side of the female thread portion, and an annular tip surface that runs along a direction approximately perpendicular to the longitudinal direction.

According to the present invention, the pile and the joint member are in contact with each other in a pressing state at the shoulder, which allows a large torque to be generated, and prestress due to compressive stress is generated, maintaining a strong connection, and preventing the connection from coming loose even in the case of a rotary pile construction method that involves repeated forward and reverse rotation.

1 is a cross-sectional view showing a pile joint structure according to one embodiment of the present invention together with an enlarged view of a portion indicated by a dashed dotted circle. FIG. 2 is a cross-sectional view of the exploded state of FIG. 1 . FIG. 13 is an enlarged view of a main portion showing an example in which a pile-side shoulder portion and a joint member-side shoulder portion are inclined surfaces. 4 is a graph showing the relationship between tightening torque and rotation angle. 1 is a graph showing the relationship between load and displacement in a tensile test. 1 is a graph showing the relationship between load and displacement in a compression test. 1 is a graph showing the relationship between bending moment and displacement in a bending test.

Hereinafter, a pile joint structure according to an embodiment of the present invention will be described.
1 and 2 show one embodiment of the present invention.
In this embodiment, the piles 10A and 10B are preferably formed into a cylindrical shape having a diameter of 200 mm to 600 mm, a length of 1.0 m or more, and a thickness of 6 mm or more, using, for example, SKK (steel pipe pile) material or STK (general structural carbon steel pipe) material conforming to the JIS standard. Of course, the piles are not limited to these materials and dimensions.
A tapered male screw portion 11 that gradually reduces in diameter toward the tip is formed on the outer peripheral surface of both ends of the piles 10A, 10B, and a coupling member 20 screwed into this male screw portion 11 connects the tips of the two piles 10A, 10B to each other.

The male threaded portion 11 of the piles 10A, 10B is formed near the middle of the thickness of the piles 10A, 10B, and a cylindrical portion 12 is formed on the base end side of the male threaded portion 11 along the longitudinal direction of the piles 10A, 10B, and a pile-side shoulder portion 13 consisting of an annular plane along a direction perpendicular to the longitudinal direction of the piles 10A, 10B is formed at the base end position of the cylindrical portion 12. In the example shown in Fig. 1, the pile-side shoulder portion 13 is formed parallel to a direction perpendicular to the longitudinal direction of the piles 10A, 10B (the radial direction of the piles 10A, 10B), in other words, perpendicular to the longitudinal direction. On the other hand, a cylindrical portion 14 is formed at the tip of the piles 10A, 10B along the longitudinal direction of the piles 10A, 10B, and the tip surface of the cylindrical portion 14 is formed into an annular tip surface 15 that is parallel to the direction perpendicular to the longitudinal direction of the piles 10A, 10B (the radial direction of the piles 10A, 10B), that is, perpendicular to the longitudinal direction of the piles 10A, 10B.
The male threads 11 of both piles 10A, 10B have the same winding direction and are formed with the same pitch.

On the other hand, the joint member 20 is made of, but is not limited to, JIS standard SN (steel material for architectural construction) material or the like, and is formed into a relatively short cylindrical shape having a length of 10 cm to 20 cm.
A female screw portion 21 that can be screwed into the male screw portion 11 of the piles 10A, 10B is formed on the inner peripheral surface at both ends of the joint member 20. Since the male screw portion 11 of the piles 10A, 10B is formed in a tapered shape, the female screw portion 21 of the joint member 20 is also formed in a tapered shape (a tapered shape that gradually increases in diameter toward the tip) that matches the male screw portion 11 of the piles 10A, 10B.

In addition, a cylindrical portion 22 is formed on the base end side of the female threaded portion 21 of the coupling member 20 along the longitudinal direction of the coupling member 20, and a coupling member side shoulder 23 portion consisting of an annular plane along a direction perpendicular to the longitudinal direction of the coupling member 20 is formed at the base end position of this cylindrical portion 22. In the example shown in FIG. 1, this coupling member side shoulder portion 23 is formed parallel to the direction perpendicular to the longitudinal direction of the coupling member 20 (the radial direction of the coupling member 20), in other words, perpendicular to the longitudinal direction. In this case, since the female threaded portion 21 is formed on both ends of the coupling member 20, the coupling member side shoulder portion 23 is arranged on the base end side of both female threaded portions 21 with their respective faces facing the tip direction. The two coupling member side shoulder portions 23 are arranged in a so-called back-to-back state.

On the other hand, at the tip of the joint member 20, a cylindrical portion 24 is formed along the longitudinal direction of the joint member 20, continuing from the female thread portion 21, and the tip surface of the cylindrical portion 24 is formed into an annular tip surface 25 that is parallel to the direction perpendicular to the longitudinal direction of the joint member 20 (the radial direction of the joint member 20), i.e., perpendicular to the longitudinal direction of the joint member 20.

This joint member 20 has two female threaded portions 21 and cylindrical portions 22, 24 formed at both ends of each female threaded portion 21. When the female threaded portions 21 are screwed into the male threaded portions 11 of the two piles 10A, 10B to connect the two piles 10A, 10B, these four cylindrical portions 22, 24 are positioned radially outward of the cylindrical portions 12, 14 of the two piles 10A, 10B. Both female threaded portions 21 of the joint member 20 have the same winding direction and are formed with the same pitch.

The distance L1 between the pile-side shoulder portion 13 and the annular tip surface 15 of the piles 10A and 10B is set to be approximately the same as the distance between the joint member-side shoulder portion 23 and the annular tip surface 25 at both ends of the corresponding joint member 20. The length L2 between the two joint member-side shoulder portions 23 of the joint member 20 is set to an appropriate length that can support the pressing force during connection described below, for example, 1.5 cm to 5.0 mm. These dimensions are not particularly limited.

The contact surface between the pile side shoulder 13 and the annular tip surface 25 of the joint member 20 and the contact surface between the joint member side shoulder 23 and the annular tip surface 15 of the pile 10A may be formed to have the same radial width, but it is preferable to make the contact surface between the pile side shoulder 13 and the annular tip surface 25 of the joint member 20 larger than the contact surface between the joint member side shoulder 23 and the annular tip surface 15 of the pile 10A, since this allows the joint member 20 to be formed thicker and stronger.

The friction coefficient μ between the shoulder portion 13, 23 and the annular tip surface 15, 25 is preferably large, and a general pickling process is recommended as a finishing process. For example, μ = 0.25 or more is desirable. The bonder process used for joining oil well pipes has a small friction coefficient of about 0.15, making it difficult to apply a large torsional torque.

When two piles 10A, 10B are connected using this joint member 20, the female threaded portion 21 on one (lower) of the joint member 20 is rotated and screwed into the male threaded portion 11 on the end of one pile (leading pile) 10A, and the torque (torsion torque) increases rapidly when both the pile side shoulder portion 13 and the annular tip surface 25 of the joint member 20 and the joint member side shoulder portion 23 and the annular tip surface 15 of the pile 10A come into contact, or when either one comes into contact first. If either one comes into contact first, the other will then come into contact, further increasing the torque. Then, by further rotating the joint member 20 in this abutting state and firmly tightening the two together, a large compressive force is applied in the longitudinal direction to the abutment surface between the pile side shoulder portion 13 and the annular tip surface 25 of the joint member 20, and to the abutment surface between the joint member side shoulder portion 23 and the annular tip surface 15 of the pile 10A.

Next, the male threaded portion 11 at the end of the other pile (the trailing pile) 10B is rotated and screwed into the other (upper) female threaded portion 21 of the joint member 20, and the joint member side shoulder portion 23 is brought into contact with the annular tip surface 15 of the pile 10A. At the same time, or slightly before or after this, the annular tip surface 25 of the joint member 20 is brought into contact with the pile side shoulder portion 13, and the pile 10B is further rotated to firmly tighten the two together, applying a longitudinal pressure force between the joint member side shoulder portion 23 and the annular tip surface 15 of the pile 10A, and between the pile side shoulder portion 13 and the annular tip surface 25 of the joint member 20, which are in contact with each other.

The two piles 10A, 10B connected in this way are joined to the joint member 20 by the tapered male thread portion 11 and female thread portion 21, and the annular tip surface 25 of the joint member 20 abuts in a pressing state against the pile side shoulder portion 13 of each pile 10A, 10B, and the annular tip surface 15 of each pile 10A, 10B abuts in a pressing state against the two joint member side shoulder portions 23. This pressing state becomes greater as the tightening force between the male thread portion 11 and the female thread portion 21 increases, and the frictional force of the abutting surfaces allows for connection with a powerful torque.

In addition, the pressing force of the contact surface between the joint member side shoulder portion 23 and the annular tip surface 15 of the pile 10A, and the contact surface between the pile side shoulder portion 13 and the annular tip surface 25 of the joint member 20 generates prestress (compressive stress) along the longitudinal direction in the piles 10A, 10B and the joint member 20, maintaining a strong connection against tension.

These synergistic effects prevent the connection between the piles 10A, 10B and the joint member 20 from coming loose, even during the rotary pile construction method, which involves repeated forward and reverse rotation. The rotary pile construction method is a construction method in which piles are driven into the ground while repeatedly rotating forward and reverse. Piles joined with this joint structure maintain a strong connection during both forward and reverse rotation, allowing for smooth and rapid on-site construction.

Of course, since it is a screw connection, it can be removed when necessary, such as in the event of an abnormality.
Furthermore, since no welding is required, costs can be reduced and on-site construction becomes easier.

Fig. 3 shows a modified joint structure, in which elements common to Fig. 1 are given the same reference numerals to simplify the explanation.
In this joint structure, the pile-side shoulder portion 13 of the piles 10A, 10B and the joint member-side shoulder portion 23 of the joint member 20 are formed to be inclined in a direction that reduces the angle with the tapered surface of the male thread portion 11 or the female thread portion 21 with respect to a direction perpendicular to the longitudinal direction of the piles 10A, 10B and the joint member 20. The annular tip surface 25 of the joint member 20 and the annular tip surface 15 of the piles 10A, 10B that abut against these shoulder portions 13, 23 are also inclined at the same angle as the shoulder portions 13, 23 to correspond to them.
The inclination angle θ is set to, for example, 5° to 10° with respect to a direction perpendicular to the longitudinal direction of the piles 10A, 10B and the joint member 20.

In such a joint structure, when a tensile force acts on the piles 10A and 10B, the joint between the tapered male thread 11 and female thread 21 maintains the threaded engagement near the center in the longitudinal direction, but a force acts in the direction of separating the threads 11 and 21 at both ends. As described above, a pressing force acts in the longitudinal direction on the contact surface between the joint member side shoulder 23 and the annular tip surface 15 of the pile 10A, and on the contact surface between the pile side shoulder 13 and the annular tip surface 25 of the joint member 20. Therefore, even if a slight force acts in the direction of separating the both ends of the threads 11 and 21, the joint state can be maintained. However, as the tensile force increases, the force in the direction of separating the both ends of the threads 11 and 21 also increases.

As shown in the example in Figure 4, the shoulder portions 13, 23 and annular tip surfaces 15, 25 are inclined in a direction perpendicular to the longitudinal direction to reduce the angle with the threaded portions 11, 21. This makes it possible to prevent the two ends of the joint member 20 and the piles 10A, 10B from moving apart by contacting each other with the inclined surfaces (shoulder portions 13, 23 and annular tip surfaces 15, 25), and to maintain a strong connection over the entire length of the threaded portions 11, 21.

The present invention is not limited to the configuration of the above-described embodiment, and various changes can be made to the details of the configuration without departing from the spirit of the present invention.
Various dimensions can also be changed depending on the required performance. If the diameter of the pile is large, this can be achieved by increasing the number of threads or increasing the outer diameter of the joint member (thickening the plate thickness).

The results of tests conducted to verify the effectiveness of this joint structure will now be described.
FIG. 4 is a graph showing the relationship between the tightening torque and the rotation angle. The position where the male threaded portion and the female threaded portion finish screwing together (the position where either the pile side shoulder portion and the annular tip surface of the coupling member, or the coupling member side shoulder portion and the annular tip surface of the pile, or both, come into contact with each other) is defined as the rotation angle of 0°. After tightening, the torque change was measured by reversing the rotation for each of the cases where the screw was further rotated 30° from the end position and tightened, rotated 5° and tightened, and rotated 1° and tightened.

The pile used was made of SKK material, with a diameter of 267.4 mm, a thickness of 9.0 mm, and a distance L1 between the pile shoulder and the annular tip surface of 5.0 cm. The joint member was made of SN material, and the distance L2 along the longitudinal direction between the shoulders of both joint members was 2.5 cm. The joint member had an outer diameter of 270.4 mm and a thickness of 12 mm.
For the specimens in which fastening was stopped at the end of the screwing, it can be said that the strength of the base material was measured.

According to Figure 4, when the screw is tightened to 30°, as the threaded portion is screwed in, either the pile shoulder and the annular tip surface of the joint member, or the joint member shoulder and the annular tip surface of the pile come into contact first (rotation angle is 0°), causing the torque to rise sharply, and then the other comes into contact, causing the torque to rise further. The torque is almost at its maximum (approximately 100 kNm) when the rotation angle is around 20°.

When reverse torque is applied after tightening to 30°, the screw does not loosen between -100kNm and -80kNm, but begins to loosen at around -80kNm (the rotation angle decreases from 30°). In other words, it can be seen that the screw does not loosen until a reverse torque of about 80% of the forward torque of 100kNm is applied.

On the other hand, when the tightening torque is small (for example, when tightened by 5°), it can be seen that the screw begins to loosen from the early stages of reversal. This is because the contact pressure between the pile shoulder and the annular tip surface of the joint member, and between the joint member shoulder and the annular tip surface of the pile, is small. However, this method can be applied to piles that do not require a large torque, such as the example of 30° rotation. It can also be used for buried piles, etc., rather than rotary pile construction, to provide an inexpensive joining method.

Fig. 5 shows load-displacement curves when a tensile test was conducted in the cases where the screw was stopped at the end of engagement of the threaded portion (no tightening), where the screw was further tightened by rotating it 30° from the end of engagement, and where the screw was further tightened by rotating it 5°.
It can be seen that in the case of fastening with a 30° rotation, the rigidity during the tensile test is large, and the yield strength σy is also large. It is assumed that the displacement associated with an increase in load is small because a compressive prestress is generated by fastening. The yield strength of this joint is smaller than that of the base material (SKK material), but it does not break down until it reaches the yield load of the base material. It can be said that this joint has the ability to elongate.
In the case of tightening with a 5° rotation, the tensile load is somewhat smaller because the prestress compressive force is smaller.

FIG. 6 shows a load-displacement curve when a compression test was carried out.
In the case of the compression test, when the joint was tightened by rotating 30 degrees, the rigidity was not much different from the others, but the yield strength was slightly smaller because the shoulder part yielded due to the tightening torque. The strength of the joint continued to increase up to the maximum load of the base material, and did not break.
In the case of tightening with a 5° rotation, the prestress is small and the shoulder portion does not yield, so the yield load does not decrease, but the strength increases to the maximum load of the base material.

Fig. 7 is a graph showing the relationship between bending moment and displacement (vertical displacement) when a bending test was performed. In the case of fastening with a 30° rotation and fastening with a 5° rotation, the characteristics are almost the same as those of the base material, and the maximum load can also exert the full plastic bending moment of the base material (Mp = σy × Zp).
In the case of fastening with a 5° rotation, the full plastic moment of the steel pipe base material can be exerted in the same manner as in the case of fastening with a 30° rotation.

10A, 10B Pile 11 Male threaded portion 12, 14 Cylindrical portion 13 Pile-side shoulder portion 13 Shoulder portion 15 Annular tip surface 20 Joint member 21 Female threaded portion 22, 24 Cylindrical portion 23 Joint member-side shoulder portion 25 Annular tip surface

Claims (2)

A joint structure for piles in which the ends of two piles are connected to each other by a joint member, the end of the pile being formed with a tapered male screw portion that gradually reduces in diameter toward the tip, a pile-side shoulder portion that forms an annular plane that extends along a direction substantially perpendicular to the longitudinal direction of the pile at the base end side of the male screw portion, and an annular tip surface that extends along a direction substantially perpendicular to the longitudinal direction of the pile at the tip of the pile,
The joint member is formed in a cylindrical shape, and at both ends thereof, a female threaded portion that screws into the male threaded portion of the pile, a joint member side shoulder portion that forms an annular plane along a direction substantially perpendicular to the longitudinal direction of the joint member at the base end side of the female threaded portion, and an annular tip surface that extends along a direction substantially perpendicular to the longitudinal direction of the joint member at the tip of the joint member,
When the male threaded portion and the female threaded portion are screwed together, the annular tip surface of the joint member is in a pressed state against the pile shoulder portion, and the annular tip surface of the pile is in a pressed state against the joint member shoulder portion,
A pile joint structure, characterized in that the abutment surface between the annular tip surface of the joint member and the pile side shoulder portion has a width dimension along the radial direction larger than that of the abutment surface between the annular tip surface of the pile and the joint member side shoulder portion . The pile joint structure described in claim 1, characterized in that the pile side shoulder portion and the annular tip surface of the pile are formed with an inclination in a direction that reduces the angle with the tapered surface of the male thread portion or female thread portion, and the joint member side shoulder portion and the annular tip surface of the joint member are formed with an inclination to match the pile side shoulder portion and the annular tip surface of the corresponding pile.