Patent Publication Number: US-2004047693-A1

Title: Joining structure of pile

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention concerns a pile connecting structure, more specifically a pile connecting structure of high workability capable of connecting upper pile and lower pile to each other simply and accurately.  
       [0002] Conventionally, as pile connecting structure for connecting upper pile and lower pile to each other, the following methods, etc. are widely adopted:  
       [0003] (1) Method of connecting the end plates of upper pile and lower pile to each other.  
       [0004] (2) Method of providing a flange joint in projection at the outer circumference of the end plates, and tightening those flange joints facing each other by means of bolt &amp; nut.  
       [0005] (3) Method of providing a pair of inner fitting and outer fitting distributed on both sides at the end of the upper pile and at the end of the lower pile, and forming threaded part on both the inner fitting and the outer fitting, to connect the inner fitting and the outer fitting to each other by screwing.  
       [0006] By the way, the conventional pile connecting structures for connecting upper pile and lower pile to each other mentioned above have the following problems respectively:  
       [0007] (1) A pile connecting structure by welding presents such problems as necessity of much time for welding, impossibility of welding work at the field of execution depending on the weather condition. Moreover, to prevent weld defects or embrittlement of weld, prescribed equipment and facilities and skilled technicians are required, and this is liable to be rather costly or cause a shortage of technicians.  
       [0008] (2) In a connecting method by flange joint, the outside diameter of the joint portion is larger than the outside diameter of the steel pipe pile and greatly protrudes from the outer circumferential face of the steel pipe pile. As a result, a large penetration resistance is produced when the piles are buried in the ground, a bending moment acts on the joint part and, moreover, an open space is produced at the outer circumference of the piles between the joints, presenting a risk of impossibility of securing the required horizontal supporting force.  
       [0009] (3) A pile connecting structure for connecting the inner fitting and the outer fitting, provided at the end of the upper pile and at the end of the lower pile, to each other by screwing leads to high cost of machining for forming threaded part on the inner fitting and the outer fitting of larger diameter. Furthermore, the connecting work by screwing of piles which are heavy materials is rather poor in workability, and requires a lot of time and labor and, in addition, the threaded part formed on the inner fitting and the outer fitting is liable to be damaged, making the connecting work by screwing difficult in this last case.  
       SUMMARY OF THE INVENTION  
       [0010] The objective of the present invention, realized in view of various problems with said conventional pile connecting structures, is to provide a pile connecting structure of high workability capable of simply and accurately connecting the upper and lower piles to each other, and preventing the pile diameter from becoming large, even at the connection portion.  
       [0011] To achieve said objective, the pile connecting structure according to the present invention is a pile connecting structure for connecting upper and lower piles to each other by interposing a connecting plate of approximately the same diameter as the piles at the connection portion between the upper and lower piles, characterized in that the end plate on either one of the upper or lower piles and the connecting plate are fixed by screwing bolts inserted into circular-shaped bolt insertion holes formed on the connecting plate to the end plate of the pile on one side, and the end plate of the other pile and the connecting plate are fixed in the state where the heads of the bolts screwed to the pile on the other side is inserted into the large diameter portion of the heteromorphic bolt insertion holes communicating between a large diameter portion which the heads of the bolts formed on the connecting plate can pass through, and a small diameter portion which the heads of the bolts cannot pass through, by making the other pile and the connecting plate move in a relative fashion so that the bolts may shift from the large diameter portion of the heteromorphic bolt insertion holes to the small diameter portion.  
       [0012] This pile connecting structure is capable of fixing, in a pile connecting structure for connecting upper and lower piles to each other, the end plates of the upper and lower piles and the respective connecting plates to each other by bolting, and by interposing a connecting plate of approximately the same diameter as the piles at the connecting portion between the upper and lower piles, thus quickly enabling the establishment of a connection between the upper and lower piles at low cost, without having any influence on pile length thanks to the comparatively small thickness of the connecting portion, and further enabling the burying of piles in the ground without presenting any obstacle to the pile driving work, thanks to the absence of any projections at the outer circumference of the piles.  
       [0013] For such cases, at the outer circumference of the connecting plate, a cylindrical body is integrally disposed in which the end of the upper and lower piles may be inserted.  
       [0014] This helps reinforce the end portions of the upper and lower piles to be connected to each other, and increases their bending strength, enabling the prevention of breaking at the connecting portion of the piles even if a strong bending force acts on the connected portion, and facilitating centering of the upper and lower piles.  
       [0015] Moreover, there may be formed on the connecting plate an operating port for fastening, from the outer circumferential side of the connecting plate, the bolts shifted from the large diameter portion of the heteromorphic bolt insertion holes to the small diameter portion.  
       [0016] This makes it possible to firmly fix the end plate of the pile on the other side and the connecting plate to each other.  
       [0017] Furthermore, the connecting plate may be formed by being split into a plurality of pieces.  
       [0018] This enables reduction of the shape of the unit component members constituting the connecting plate and reduces their weight, thus improving workability and handling ease.  
       [0019] Also, on the connecting plates of the piles, there may be disposed an auxiliary member having a threaded hole different from that of the connecting plate, so that the pile connecting bolts may be screwed into that auxiliary member.  
       [0020] This makes it possible to freely change the diameter, the number of pieces, etc. of the bolts used for the connection of piles, and improve the strength of the end part of the piles.  
       [0021] Moreover, in place of bolts, projections in the shape of bolts may be provided in a way that they can be fixed to either the end parts of the piles or the auxiliary members.  
       [0022] This enables the promotion of diversification of the members. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023]FIG. 1 indicates the first embodiment of the pile connecting structure according to the present invention, (A) being a bottom view, (B) a sectional view at line A-B of (A), and (C) a sectional view at line B-C of (A).  
     [0024]FIG. 2 indicates the sequence of execution of the first embodiment of the pile connecting structure according to the present invention, (A) being a sectional view showing the state of fixing of the lower pile and the connecting plate, and (B) a sectional view showing the state of fixing of the lower pile and the connecting plate on the left half and that of the upper pile and the connecting plate on the right half, respectively.  
     [0025]FIG. 3 indicates the second embodiment of the pile connecting structure according to the present invention, (A) being a bottom view, (B) a sectional view at line X-X of (A), (C) a sectional view at line A-B of (A), and (D) a sectional view at line B-C of (A).  
     [0026]FIG. 4 indicates the sequence of execution of the second embodiment of the pile connecting structure according to the present invention, (A) being a sectional view showing the state of fixing of the lower pile and the connecting plate, and (B) a sectional view showing the state of fixing of the lower pile and the connecting plate on the left half and that of the upper pile and the connecting plate on the right half, respectively.  
     [0027]FIG. 5 is an exploded perspective view of the second embodiment of the pile connecting structure according to the present invention.  
     [0028]FIG. 6 is an expanded sectional view of an end plate of pile in the second embodiment of the pile connecting structure according to the present invention.  
     [0029]FIG. 7 indicates an example in which the connecting plate (cylindrical body) is split in the circumferential direction, (A) being a bottom view, and (B) a sectional view at line A-B of (A).  
     [0030]FIG. 8 is a perspective view for above.  
     [0031]FIG. 9 indicates an example in which the connecting plate (cylindrical body) is split in the horizontal direction, (A) being a bottom view, (B) a sectional view at line X-X of (A), and (C) a sectional view at line A-B of (A).  
     [0032]FIG. 10 is a perspective view of the example in which the connecting plate (cylindrical body) is split in the horizontal direction.  
     [0033]FIG. 11 indicates an example in which auxiliary member is disposed on the end place of pile, (A) being a sectional view before connection, and (B) a sectional view showing the connected state. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0034] Embodiments of the pile connecting structure according to the present invention will be explained hereafter based on drawings.  
     [0035]FIG. 1 to FIG. 2 indicate the first embodiment of the pile connecting structure according to the present invention.  
     [0036] This pile connecting structure is a pile connecting structure for connecting an upper pile  1  and a lower pile  3  to each other, by interposing a connecting plate  5  of about the same diameter as the piles, at the connecting portion between the upper pile  1  and the lower pile  3 , wherein the end plate  4  of either one of the upper pile  1  or lower pile  3 , lower pile  3  in this embodiment, and the connecting plate  5  are fixed by screwing bolts  6  inserted in circular bolt inserting holes  51  formed on the connecting plate  5  to the bolt holes  41  in the end plate  4  of the lower pile  3 , and the end plate  2  of the other pile, upper pile  1  in this embodiment, and the connecting plate  5  are fixed, in the state in which the head  71  of the bolts  7  screwed to the end plate  2  of the upper pile  1  is inserted in the large diameter portion  52   d  of heteromorphic bolt insertion holes  52  communicating between a large diameter portion  52   d  which the head  71  of the bolts  7  formed on the connecting plate  5  can pass through and a small diameter portion  52   c  which the head  71  of the bolts  7  cannot pass through, by making the upper pile  1  and the connecting plate  5  move relatively, in the state in which the connecting plate  5  is fixed in the lower pile  3  so that the bolts  7  may shift from the large diameter portion  52   d  of the heteromorphic bolt insertion holes  52  to the small diameter portion  52   c.    
     [0037] The piles to which can be applied this pile connecting structure are concrete piles such as prestressed concrete piles, etc., steel piles, SC piles, and composite piles such as PRC piles, etc. provided with end plate at the end, though not particularly restricted to them. Explanation will be given below by taking an example of prestressed concrete piles.  
     [0038] The upper pile  1  and lower pile  3  consisting of prestressed concrete piles have end plates  2 ,  4  disposed at their end, and in these end plates  2 ,  4  are formed bolt holes  21 ,  41  which were used for introducing prestressed (concrete) when manufacturing prestressed concrete piles. Those bolt holes  21 ,  41  are utilized in this embodiment.  
     [0039] The bolt holes  21 ,  41  may be newly formed separately from the bolt holes used for introducing prestressed (concrete), as a matter of course.  
     [0040] The connecting plate  5  has a donut shape of about the same diameter as that of the upper pile  1  and lower pile  3 , more concretely the end plates  2 ,  4  of the upper pile  1  and lower pile  3  are manufactured with steel sheet (including molded sheet) of a thickness about 1.5 to 2 times the heads  61 ,  71  of the bolts  6 ,  7 , for example, though not particularly restricted to it.  
     [0041] On the connecting plate  5  are formed bolt holes  51  at the position corresponding to the bolt holes  41  formed in the end plate  4  of the lower pile  3 , and at proper position between those bolt holes  51  are formed bolt holes  52  at the position corresponding to the bolt holes  21  formed in the end plate  2  of the upper pile  1 .  
     [0042] These bolt holes  51 ,  52  are formed on one face of the connecting plate  5  respectively, preferably alternately in the circumferential direction, though not particularly restricted to it.  
     [0043] And, the bolt holes  51  will be provided with a bolt head inserting portion  51   a  formed deeper than the height of the head  61  of the bolt  6 , as shown in FIGS.  1 (A), (B), so that the head  61  of the bolt  6  may be inserted without being exposed to outside.  
     [0044] This bolt head inserting portion  51   a  will be formed in a size enabling to tighten the bolt  6  by fitting a box wrench (not illustrated) at the head  61  of the bolt  6 .  
     [0045] This makes it possible to prevent the top face of the head  61  of the bolt  6  from getting in contact with the end plate  2  of the upper pile  1 , when the end plate  4  of the lower pile  3  and the connecting plate  5  are fixed and the end plate  2  of the upper pile  1  is placed on it.  
     [0046] Moreover, the bolt holes  52  will be in a heteromorphic shape like that of a snowman communicating between a large diameter portion  52   d  which the head  71  of the bolts  7  can pass through and a small diameter portion  52   c  which the head  71  of the bolts  7  cannot pass through, and be provided with a bolt head inserting portion  52   a  formed deeper than the height of the head  71  of the bolt  7 , so that the head  71  of the bolt  7  may be inserted without being exposed, as shown in FIGS.  1 (A), (C).  
     [0047] This makes it possible to prevent the bottom face of the head  71  of the bolt  7  from getting in contact with the end plate  4  of the lower pile  3 , when the end plate  2  of the upper pile  1  and the connecting plate  5  are fixed through the bolt  7 .  
     [0048] This bolt insertion holes  52  will be provided on the outer circumferential side of the connecting plate  5 , so that it may also serve as an operating port So for fastening the bolt  7  shifted from the large diameter portion  52   d  of the bolt insertion hole  52  to the small diameter portion  52   c,  from outside the outer circumference of the connecting plate  5 , by inserting a tool S such as spanner, etc.  
     [0049] Furthermore, to prevent detachment, etc. of the connecting portion with loosening of bolt  7  or relative reverse turn of the upper pile  1  and the connecting plate  5 , it is desirable to fit a wedge-shaped filler made of metal piece, etc., for example, in the open space of the large diameter portion  52   d  through the operating port So from outside the outer circumference of the connecting plate  5 , after shifting the bolt  7  from the large diameter portion  52   d  of the bolt insertion hole  52  to the small diameter portion  52   c,  to fill the open space of the large diameter portion  52   d.    
     [0050] Instead of opening the bolt insertion hole  52  on the outer circumferential side of the connecting plate  5  (form an operating port So), it may be all right to construct (the bolt insertion hole  52 ) in a way to either make the bolt  7 , the head  71  of which is inserted in the large diameter portion  52   d  of the heteromorphic bolt insertion hole  52 , turn in the fastening direction, when shifting it from the large diameter portion  52   d  to the small diameter portion  52   c  of the heteromorphic bolt insertion hole  52 , with the difference in contact resistance between the bolt seating face  52   b  and the head  71  of the bolt  7  [To make the contact resistance between the bolt seating face  52   b  on the outer circumference side of the connecting plate  5  and the head  71  of the bolt  7  larger than that on the inner circumference side of the connecting plate  5  (case where the bolt  7  is right threaded, in this embodiment) (or smaller (case where the bolt  7  is left threaded, in this embodiment)), either perform surface treatment to the bolt seating face  52   b,  or dispose a member increasing the contact resistance such as soft metal plate such as aluminium, etc. or synthetic resin plate, etc. on the bolt seating face  52   b ], or form the height of the bolt seating face  52   b  on the large diameter portion  52   d  side and the small diameter portion  52   c  side of the heteromorphic bolt insertion hole  52  in a way to become gradually higher from the large diameter portion  52   d  side toward the small diameter portion  52   c  side and shift the bolt  7 , the head  71  of which is inserted in the large diameter portion  52   d  of the heteromorphic bolt insertion hole  52 , from the large diameter portion  52   d  to the small diameter portion  52   c  of the heteromorphic bolt insertion hole  52 , so that the bolt  7  may be seated on the bolt seating face  52   b  at the position of the small diameter portion  52   c  of the heteromorphic bolt insertion hole  52 .  
     [0051] This makes it possible to firmly fix the end plate  2  of the upper pile  1  and the connecting plate  5  to each other.  
     [0052] Next, explanation will be given on the method for connecting the upper pile  1  and the lower pile  3  to each other, by using this connecting plate  5 .  
     [0053] As shown in FIG. 2(A), install the lower pile  3  in a pile hole dug in the ground and, in the state in which the lower pile  3  is provisionally fixed so that the lower pile  3  may not make any up-down movement or turn, when the end plate  4  disposed at the end part of the lower pile  3  reached a prescribed position from the ground such as a height easy for execution of work by workers on the ground, for example, though not particularly restricted to it, place the connecting plate  5  concentrically on the end plate  4  of the lower pile  3 , make the bolt hole  41  formed in the end plate  4  agree with the bolt insertion hole  51  in the connecting plate  5 , insert the bolt  6  in the bolt insertion hole  51 , and fit the bolt  6  in the bolt hole  41  by screwing, by using a box wrench (not illustrated).  
     [0054] This makes it possible to prevent the top face of the head  61  of the bolt  6  from getting in contact with the end plate  2  of the upper pile  1 , when the end plate  4  of the lower pile  3  and the connecting plate  5  are fixed to each other through the bolt  6  and the end plate  2  of the upper pile  1  is placed on it.  
     [0055] The fixing work of the end plate  4  of the lower pile  3  and the connecting plate  5  may be performed before the lower pile  3  is installed in the pile hole.  
     [0056] Next, as shown in FIG. 2(B), lift and let down the upper pile  1  on the connecting plate  5  fixed to the end plate  4  of the lower pile  3 , by using a crane, etc., in a way to be concentric with the lower pile  3 , for installation.  
     [0057] At that time, screw the bolt  7  in advance, in the bolt hole  21  in the end plate  2  of the upper pile  1 , and, in the state in which the head  71  of the bolt  7  is positioned to the large diameter portion  52   d  of the heteromorphic bolt insertion hole  52  formed in the connecting plate  5 , lift and let down the upper pile  1 , so that the head  71  of the bolt  7  may be inserted in the large diameter portion  52   d  of the heteromorphic bolt insertion hole  52 .  
     [0058] In screwing the bolt  7  in the bolt hole  21  in the end plate  2  of the upper pile  1 , set the amount of projection of the bolt head  71 , in a way to secure a small clearance between the seating face of the bolt head  71  and the bolt seating face  52   b  of the bolt insertion hole  52 , so that the bolt  7  may be shifted from the large diameter portion  52   d  to the small diameter portion  52   c  of the heteromorphic bolt insertion hole  52 , in the state in which the bolt head  71  is inserted in the large diameter portion  52   d  of the bolt insertion hole  52 . It will be so arranged that the bottom face of the head  71  of the bolt  7  may not get in contact with the end plate  4  of the lower pile  3 , when the end plate  2  of the upper pile  1  and the connecting plate  5  are fixed to each other through the bolt  7 .  
     [0059] And, in the state in which the bolt head  71  of the bolt  7  screwed in the end plate  2  of the upper pile  1  is inserted in the large diameter portion  52   d  of the heteromorphic bolt insertion hole  52 , shift the bolt  7  from the large diameter portion  52   d  to the small diameter portion  52   c  of the heteromorphic bolt insertion hole  52 , by making the upper pile  1  and the connecting plate  5  relatively turn to move (upper pile  1  in the case of this embodiment) in the state where the connecting plate  5  is fixed to the lower pile  3 .  
     [0060] After that, fasten the bolt  7  shifted to the small diameter portion  52   c  of the bolt insertion hole  52 , from outside the outer circumference of the connecting plate  5 , through the operating port (bolt insertion holes  52 ) provided on the outer circumferential side of the connecting plate  5 , by inserting a tool S such as spanner, etc., to firmly fix the end plate  2  of the upper pile  1  and the connecting plate  5  to each other through the bolt  7 .  
     [0061] As described above, the upper pile  1  and the lower pile  3  can be fixed with the bolt  6  and the bolt  7  respectively, by interposing one piece of connecting plate  5  at the connecting portion between the two, enabling to perform the connection between upper pile  1  and lower pile  3  quickly and at low cost, without having any influence on the pile length because the thickness of the connecting portion can be kept comparatively small. In addition, absence of any projection at the outer circumference of the piles makes it possible to bury the piles in the ground without putting any obstacle to the pile driving work, and execute the piles with high reliability and accuracy and efficiently.  
     [0062] Next, the second embodiment of the pile connecting structure according to the present invention is indicated in FIG. 3 to FIG. 6.  
     [0063] This pile connecting structure is identical to said pile connecting structure of first embodiment in that it is a pile connecting structure for connecting an upper pile  1  and a lower pile  3  to each other, by interposing a connecting plate  5  of about the same diameter as the piles, at the connecting portion between the upper pile  1  and the lower pile  3 , wherein the end plate  4  of either one of the upper pile  1  or lower pile  3 , lower pile  3  in this embodiment, and the connecting plate  5  are fixed by screwing bolts  6  inserted in circular bolt inserting holes  51  formed on the connecting plate  5  to the bolt holes  41  in the end plate  4  of the lower pile  3 , and the end plate  2  of the other pile, upper pile  1  in this embodiment, and the connecting plate  5  are fixed, in the state where the head  71  of the bolts  7  screwed to the end plate  2  of the upper pile  1  is inserted in the large diameter portion  52   d  of heteromorphic bolt insertion holes  52  communicating between a large diameter portion  52   d  which the head  71  of the bolts  7  formed on the connecting plate  5  can pass through and a small diameter portion  52   c  which the head  71  of the bolts  7  cannot pass through, by making the upper pile  1  and the connecting plate  5  move relatively, in the state in which the connecting plate  5  is fixed in the lower pile  3  so that the bolts  7  may shift from the large diameter portion  52   d  of the heteromorphic bolt insertion holes  52  to the small diameter portion  52   c  and, in addition to such construction, at the outer circumference of the connecting plate  5  is integrally disposed a cylindrical body  8  in which the end of the upper pile  1  and the lower pile  3  may be inserted.  
     [0064] The cylindrical body  8  will be made of steel, in the same way as the connecting plate  5 , integrally disposed on the connecting plate  5  by welding, etc. (the cylindrical body  8  may be integrally formed with the connecting plate  5 , in the case where it is made of casting), and will be formed in dimensions enabling to insert the end of the upper pile  1  and the lower pile  3  by several centimeters to tens of centimeter, though not particularly restricted to it.  
     [0065] As described above, by integrally disposing, at the outer circumference of the connecting plate  5 , the cylindrical body  8  in which the end of the upper pile  1  and the lower pile  3  may be inserted, it becomes possible to reinforce the end of the upper pile  1  and the lower pile  3  to be connected to each other, and increase their bending strength, thus preventing breaking of the connecting portion of the piles even if a large bending moment acts on the connecting portion, and facilitating centering of the upper pile  1  and the lower pile  3 .  
     [0066] By the way, in this embodiment, no operating port is formed for fastening, by inserting a tool S such as spanner, etc. from outside the outer circumference of the connecting plate  5 , the bolts  7  shifted from the large diameter portion  52   d  of the heteromorphic bolt insertion holes  52  to the small diameter portion  52   c  by making the upper pile  1  and the connecting plate  5  relatively turn to move in the state where the connecting plate  5  is fixed to the lower pile  3  (it is possible, of course, to form an operating port So to that end, in the cylindrical body  8  and the connecting plate  5 , in a way to communicate with the bolt insertion holes  52 , as shown in FIG. 3 to FIG. 4 with dotted line, and in FIG. 5 with solid line), it is possible to fix the end plate  2  of the upper pile  1  and the connecting plate  5  to each other through the bolt  7 , by simply making the upper pile  1  and the connecting plate  5  move relatively so that the bolts  7  may shift from the large diameter portion  52   d  of the heteromorphic bolt insertion holes  52  to the small diameter portion  52   c  with the connecting plate  5  fixed in the lower pile  3 , in the state in which the head  71  of the bolts  7  screwed to the end plate  2  of the upper pile  1  is inserted in the large diameter portion  52   d  of heteromorphic bolt insertion holes  52 , in combination with the arrangement of integrally disposing the cylindrical body  8  in which the end of the upper pile  1  and the lower pile  3  may be inserted.  
     [0067] In this embodiment, it is further possible to dispose a shift control means for controlling relative turn and movement of the upper pile  1  and the connecting plate  5  (also the lower pile  3  and the connecting plate  5 , as required) after shifting the upper pile  1  and the connecting plate  5  from the large diameter portion  52   d  of the bolt insertion holes  52  to the small diameter portion  52   c  by making them relatively turn and move, with the connecting plate  5  fixed in the lower pile  3 .  
     [0068] This shift control means is constructed, in this embodiment, with a bolt insertion hole  81  formed in the cylindrical body  8 , and a bolt  9  designed to be either inserted or screwed in this bolt insertion hole  81  and either screwed or fixed to the upper pile  1  (lower pile  3 ).  
     [0069] Moreover, as shown in FIG. 6, on the outer circumferential face of the end plate  2  of the upper pile  1  (the end plate  4  of the lower pile  3 ) may be formed a groove  22  (groove  42 ) in which to insert the tip of the bolt  9 , so that the upper pile  1  and the connecting plate  5  (the lower pile  3  and the connecting plate  5 ) may be fixed firmly to each other, by the bolt  9  screwed in the bolt insertion hole  81 .  
     [0070] This groove  22  (groove  42 ) may take any desired sectional shape such as U-shaped groove, etc. or may also be realized as a hole or threaded hole in which to either insert or screw the tip of the bolt  9 , in place of a groove.  
     [0071] A pin, etc. may also be used, in place of the bolt  9 , as shift control means.  
     [0072] This makes it possible to prevent detachment, etc. of the connecting portion with relative reverse turn of the upper pile  1  and the connecting plate  5  (the lower pile  3  and the connecting plate  5 ), thus ensuring fixing not only of the upper pile  1  and the connecting plate  5  (the lower pile  3  and the connecting plate  5 ) but also of the upper pile  1  and the lower pile  3 .  
     [0073] Furthermore, by disposing this shift control means, it becomes possible to set short the required dimensions for inserting the end of the upper pile  1  and the lower pile  3  in the cylindrical body  8 .  
     [0074] By the way, while, in the respective embodiments described above, the connecting plate  5  (cylindrical body  8 ) was formed as a single body, the connecting plate  5  (cylindrical body  8 ) may also be formed by splitting into a plurality of pieces.  
     [0075] As a method of splitting, the connecting plate  5  (cylindrical body  8 ) may be split into a plurality of unit component members  5 A,  5 B in the circumferential direction (vertical splitting), as shown in FIG. 7 to FIG. 8 (Split into 2 pieces in the illustrated embodiment. Splitting into 3 or more pieces is also possible. Moreover, in that case, it is desirable to construct the unit component members  5 A,  5 B in a way to share a single bolt  6 , by providing a fitting portion so that they may fit at the position of the bolt insertion holes  51 A,  51 B formed on the unit component members  5 A,  5 B, so that the integrity of the split unit component members  5 A,  5 B may be maintained easily.), or split into a plurality of unit component members  5 C,  5 D,  5 E in the horizontal direction (horizontal splitting), as shown in FIG. 9 to FIG. 10 (Split into 3 pieces in the illustrated embodiment. Splitting into 2 pieces or 4 or more pieces is also possible.).  
     [0076] By forming, as described above, the connecting plate  5  (cylindrical body  8 ) by splitting it into a plurality of unit component members, it becomes possible to reduce the shape and weight of the unit component members constituting the connecting plate  5  (cylindrical body  8 ), and thus improve its workability and ease of handling.  
     [0077] Still more, on the end plates  2 ,  4  of the upper pile  1  and the lower pile  3  may be disposed auxiliary members  2 A,  4 A having threaded hole different from that of the end plates  2 ,  4 , to screw the pile connecting bolt to these auxiliary members.  
     [0078] This auxiliary member will be constructed with auxiliary members  2 A,  4 A of the same shape as end plates  2 ,  4  disposed along the end plates  2 ,  4  of the upper pile  1  and the lower pile  3 , as shown in FIG. 11, for example, and the auxiliary members  2 A,  4 A will be integrated with the end plates  2 ,  4  by welding or bolting, etc.  
     [0079] By disposing, as described above, auxiliary members  2 A,  4 A having threaded hole different from that of the end plates  2 ,  4  on the end plates  2 ,  4  of the upper pile  1  and the lower pile  3  and enabling to screw the pile connecting bolts  6 ,  7  to these auxiliary members  2 A,  4 A, it becomes possible to freely change the diameter, number of pieces, etc. of the bolts used for the connection of piles, and to also improve the strength at the end of the piles.  
     [0080] The pile connecting structure according to the present invention has so far been explained based on a plurality of embodiments. However, the present invention is not restricted to the constructions indicated in the embodiments described above, but may be changed in construction as required in the extent not deviating from its purpose, by either combining the constructions indicated in the respective embodiments, or connecting the upper pile  1  and the lower pile  3  and the connecting plate  5  in different positional relations, or fixing bolt-shaped projection to the end plate of the piles by welding, fitting, etc., in place of the bolts  6 ,  7  to be screwed to the end plates  2 ,  4  of the upper pile  1  and the lower pile  3 , or extending the range of application widely to such objects as concrete piles provided with end plate at end portion, steel piles, SC piles, composite piles such as PRC piles, etc., for example, in addition to the prestressed concrete piles in the above-described embodiments.  
     [0081] According to the pile connecting structure of the present invention, which is a pile connecting structure for connecting upper pile and lower pile to each other, by interposing a connecting plate of about the same diameter as the piles, at the connecting portion between the upper pile and the lower pile, and which enables to fix the end plates  2 ,  4  of the upper pile  1  and the lower pile  3  and the connecting plate  5  to each other, it becomes possible to perform the connection between upper pile  1  and lower pile  3  quickly and at low cost, without having any influence on the pile length because the thickness of the connecting portion can be kept comparatively small. In addition, absence of any projection at the outer circumference of the piles makes it possible to bury the piles in the ground without putting any obstacle to the pile driving work, and execute the piles with high reliability and accuracy and efficiently.  
     [0082] Moreover, by integrally disposing, at the outer circumference of the connecting plate, a cylindrical body in which the end of the upper pile and the lower pile may be inserted, it becomes possible to reinforce the end portion of the upper pile and the lower pile to be connected to each other, and increase their bending strength, enabling to prevent breaking of the connecting portion of the piles even if a large bending moment acts on the connecting portion, and facilitating centering of the upper and lower piles.  
     [0083] Furthermore, by forming, on the connecting plate, an operating port for fastening, from the outer circumferential side of the connecting plate, the bolts shifted from the large diameter portion of the heteromorphic bolt insertion holes to the small diameter portion, it becomes possible to firmly fix the end plate of the pile on the other side and the connecting plate to each other.  
     [0084] Still more, by forming the connecting plate by splitting into a plurality of pieces, it becomes possible to reduce the shape of the unit component members constituting the connecting plate and reduce their weight, thus improving workability and ease of handling.  
     [0085] Yet more, by disposing, on the connecting plate of piles, an auxiliary member having a threaded hole different from that of the connecting plate, so as to screw the pile connecting bolt in that auxiliary member, it becomes possible to freely change the diameter, number of pieces, etc. of the bolts used for the connection of piles, and improve the strength of the end part of piles.  
     [0086] In addition, by providing, in place of bolts, projections in the shape of bolts in a way to be fixed to either the end part of piles or the auxiliary member, it becomes possible to promote diversification of the members.