Abstract:
An improved transition coupling for a helical soil pile assembly transfers a compression load between two coupled shaft segments with little or no compression loading on the bolts that fasten the parts together. The coupling body has a shaft-receiving socket that extends axially into the body from one end to a socket bottom that axially abuts the end of one of the shafts. The body also has at least one shoulder between its ends that extends laterally outward and faces toward the end remote from the socket. A cylindrical portion of the body, which fits closely within the hollow end of the other shaft, extends axially toward the socket end up to the shoulder, which is adapted to abut the end of that shaft. At least one pair of aligned transverse holes in the body is adapted to receive a fastener.

Description:
FIELD OF THE INVENTION 
     The present invention relates to installing piles in soil, in particular, to helical piles that are driven into soil by rotation of a shaft. 
     BACKGROUND OF THE INVENTION 
     A helical pile is a segmented deep foundation system with helical load-bearing plates usually welded to a central steel shaft. The helical plates usually have a uniform pitch and are spaced far enough apart so that they function independently as individual bearing elements. Installation typically involves driving the shaft in rotation by means of a hydraulic motor. Shaft segments (with or without load-bearing plates) may be added until a desired soil depth or load-bearing capacity is reached. 
     The central steel shafts that carry the helical bearing plates are typically square or round (i.e., circular) in cross-section. Round and square shaft segments may be used in combination, for example, in areas where soft/loose soils are located above the bearing strata (i.e., hard/dense soils) for the bearing plates. The round shaft, which has a greater section modulus, will resist columnar buckling in the soft/loose soil. The square shaft will allow adequate penetration of the helices into the hard/dense material to achieve proper load-bearing capacity without “spin-out,” i.e., loss of thrust of the helices in the soft/loose material. Shaft segments typically are joined with complicated, costly fabricated transition couplings. Bolts, which fasten the shaft segments to the coupling, bear at least some of the axial compression load. 
     SUMMARY OF THE INVENTION 
     The invention provides an improved transition coupling for helical soil pile assemblies that transfers axial compression loads between the coupled shaft segments with little or no axial compression loading on the bolts that fasten the parts together. 
     According to one aspect, the invention is directed to a coupling for connecting a hollow end of a rotatable cylindrical first shaft to an end of a second shaft, the coupling comprising a body having a first end, a second end opposite the first end, and a longitudinal axis extending between the first end and the second end. The body comprises a socket having a side wall adapted to closely receive the end of the second shaft. The socket extends axially into the body from the second end to a socket bottom facing toward the second end and adapted to axially abut the end of the second shaft. The body also comprises at least one shoulder between the first end and the second end extending laterally outward from the body and facing toward the first end. The body further comprises a cylindrical portion adapted to fit closely within the hollow end of the first shaft. The cylindrical portion extends axially from the first end toward the second end up to the shoulder, which is adapted to abut the end of the first shaft. At least one pair of aligned transverse holes in the body is adapted to receive a fastener. 
     According to another aspect, the invention is directed to a coupling for connecting a hollow end of a rotatable cylindrical first shaft to an end of a second shaft, the coupling comprising a body having a first end, a second end opposite the first end, and a longitudinal axis extending between the first end and the second end. The body comprises a socket having a side wall adapted to closely receive the end of the second shaft. The socket extends axially into the body from the second end to a socket bottom adapted to axially abut the end of the second shaft. The body also comprises a cylindrical portion extending axially from the first end toward the second end and beyond the socket bottom, and a first pair of aligned transverse holes in the side wall of the socket, which is adapted to receive a fastener. Preferably, the first pair of aligned transverse holes are in the cylindrical portion, which preferably has a second pair of aligned transverse holes adapted to receive another fastener. 
     Coupling embodiments can be configured to join two cylindrical shafts or to join two shafts having distinctly different cross-sections, such as a cylindrical shaft and a square shaft. As to all coupling embodiments, it is preferred that the body be formed as one piece by any suitable process, such as casting, forging, machining, etc., and that it taper inwardly near and toward the second end, through which the socket extends. 
     The invention also is directed to a helical soil pile assembly that incorporates any of the coupling embodiments outlined above. 
     Additional features and advantages of the invention will be apparent from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Preferred embodiments of the invention are described in detail below, purely by way of example, with reference to the accompanying drawing, in which: 
         FIG. 1  is a perspective view of a helical soil pile assembly incorporating a coupling according to a first embodiment of the invention; 
         FIG. 2  is a perspective view of the coupling of  FIG. 1 ; 
         FIG. 3  is a side elevational view of the coupling of  FIG. 1 ; 
         FIG. 4  is an end elevational view of the coupling of  FIG. 1 ; 
         FIG. 5  is a side elevational view in longitudinal cross-section of the coupling of  FIG. 1  taken along line  5 - 5  in  FIG. 3 ; 
         FIG. 6  is a side elevational view in longitudinal cross-section of the assembly of  FIG. 1  taken along line  6 - 6  in  FIG. 1 ; 
         FIG. 7  is an exploded view in longitudinal cross-section of the assembly of  FIG. 1 ; 
         FIG. 8  is a perspective view of a helical soil pile assembly incorporating a coupling according to a second embodiment of the invention; 
         FIG. 9  is a perspective view of the coupling of  FIG. 8 ; 
         FIG. 10  is a side elevational view of the coupling of  FIG. 8 ; 
         FIG. 11  is a side elevational view of the coupling of  FIG. 8  taken at 90° to  FIG. 10 ; 
         FIG. 12  is an end elevational view of the coupling of  FIG. 8 ; 
         FIG. 13  is a side elevational view in longitudinal cross-section of the coupling of  FIG. 8  taken along line  13 - 13  in  FIG. 10 ; 
         FIG. 14  is a side elevational view in longitudinal cross-section of the assembly of  FIG. 8  taken along line  14 - 14  in  FIG. 8 ; 
         FIG. 15  is a partial side elevational view of the assembly of  FIG. 8  taken at 90° to  FIG. 14 , with a portion of the cylindrical shaft broken away; 
         FIG. 16  is an exploded view in longitudinal cross-section of the assembly of  FIG. 8 ; 
         FIG. 17  is a perspective view of a helical soil pile assembly incorporating a coupling according to a third embodiment of the invention; 
         FIG. 18  is a perspective view of the coupling of  FIG. 17 ; 
         FIG. 19  is a side elevational view of the coupling of  FIG. 17 ; 
         FIG. 20  is a side elevational view of the coupling of  FIG. 17  taken at 90° to  FIG. 19 ; 
         FIG. 21  is an end elevational view of the coupling of  FIG. 17 ; 
         FIG. 22  is a side elevational view in longitudinal cross-section of the coupling of  FIG. 17  taken along line  22 - 22  in  FIG. 19 ; 
         FIG. 23  is a side elevational view in longitudinal cross-section of the assembly of  FIG. 17  taken along line  23 - 23  in  FIG. 17 ; and 
         FIG. 24  is a partial side elevational view of the assembly of  FIG. 17  taken at 90° to  FIG. 23 , with a portion of the upper cylindrical shaft broken away. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts a helical soil pile assembly  10  that incorporates a coupling  20  according to a first embodiment of the invention. Coupling  20  joins a round (cylindrical) shaft  12  to a square shaft  14 , to which at least one helical load-bearing plate  16  may be welded. Alternatively, shaft  14  may be an extension shaft devoid of load-bearing plates. As explained below, a bolt  48 , and preferably an additional bolt  52 , secure the parts together. 
     Referring to  FIGS. 2-5 , coupling  20  comprises a hollow body  22  preferably formed as one piece, preferably of iron or steel. The body is symmetrical about two mutually orthogonal planes that intersect along its central longitudinal axis. The body has a cylindrical portion  24  that extends from one end of the body to an annular shoulder  26 , which extends laterally outward. The body also has a nose portion  28  that extends from shoulder  26  to the other end of the body, tapering inwardly. The taper facilitates soil penetration during installation, minimizing soil disturbance. A substantially square socket  30  extends axially into body  22  through nose portion  28 , beyond shoulder  26  and into cylindrical portion  24 . The side wall of socket  30  comprises two pairs of opposite side walls  32  and terminates in an inner end defined by a shoulder  34  that faces toward the open end of the socket. A pair of aligned transverse holes  36  extend through socket  30  in cylindrical portion  24 . Preferably, another pair of aligned transverse holes  38  extend through cylindrical portion  24  remote from socket  30 . 
       FIGS. 6 and 7  illustrate how coupling  20  is joined to a round shaft  12  and a square shaft  14 . Cylindrical portion  24  is sized to fit closely within a round shaft  12 , with the end  40  of round shaft  12  abutting shoulder  26 . Round shaft  12  has a pair of aligned transverse holes  42  near its end  40 , and another pair of transverse holes  44  spaced further from end  40 . Socket  30  is sized to closely receive a square shaft  14 , with the end of shaft  14  abutting shoulder  34 . Square shaft  14  has a transverse hole  46  near its end. When the three parts are assembled, holes  42  in round shaft  12  align with holes  36  in body  22  and with hole  46  in square shaft  14 . A bolt  48  placed through these aligned holes is secured by a nut  50  to fasten all three parts together. In addition, transverse holes  44  in round shaft  12  align with transverse holes  38  in body  22 . A bolt  52  placed through these aligned holes is secured by a nut  54  to further secure the coupling  20  to round shaft  12 . In use, axial compression loads applied to the assembly  10  are borne almost exclusively by shoulders  26  and  34 , minimizing axial stress on fastening bolts  48 ,  52 . 
       FIG. 8  depicts a helical soil pile assembly  58  that incorporates a coupling  60  according to a second embodiment of the invention. Coupling  60  joins a round shaft  12  to a square shaft  14 , to which at least one helical load-bearing plate  16  may be welded. Alternatively, shaft  14  may be an extension shaft devoid of load-bearing plates. As explained below, bolts  84 ,  88  secure the parts together. 
     Referring to  FIGS. 9-13 , coupling  60  comprises a hollow body  62  preferably formed as one piece, preferably of iron or steel. The body is symmetrical about two mutually orthogonal planes that intersect along its central longitudinal axis. The body has a cylindrical portion  64  that extends from one end of the body to a pair of diametrically opposed arcuate shoulders  66 , which extend laterally outward. The body also has a nose portion  68  that extends from shoulders  66  to the other end of the body, tapering inwardly. The taper facilitates soil penetration during installation, minimizing soil disturbance. Two diametrically opposed flats  69  on nose portion  68  separate shoulders  66  from one another. A substantially square socket  70  extends axially into body  62  through nose portion  68 , beyond shoulders  66 . The side wall of socket  70  comprises two pairs of opposite side walls  72  and terminates in an inner end defined by a shoulder  74  that faces toward the open end of the socket. A pair of aligned transverse holes  76  extend through socket  70  in nose portion  64 , opening on flats  69 . A plurality (preferably three) pairs of aligned transverse holes  78  extend through cylindrical portion  64  remote from socket  70 . Preferably, holes  76  in nose portion  68  are wider than holes  78  in cylindrical portion  64  so as to accommodate wider bolts. 
       FIGS. 14-16  illustrate how coupling  60  is joined to a round shaft  12  and a square shaft  14 . Cylindrical portion  64  is sized to fit closely within a round shaft  12 , with the end  80  of round shaft  12  abutting shoulders  66 . Round shaft  12  has three pairs of aligned transverse holes  82 . Socket  70  is sized to closely receive a square shaft  14 , with the end of shaft  14  abutting shoulder  74 . Square shaft  14  has a transverse hole  86  near its end. When the three parts are assembled, holes  82  in round shaft  12  align with holes  78  in body  62 . A bolt  84  placed through each of these three sets of aligned holes is secured by a nut  87  to fasten round shaft  12  and coupling  60  together. In addition, hole  86  in square shaft  14  aligns with transverse holes  76  in nose portion  68 . A bolt  88  placed through aligned holes  76 ,  86  is secured by a nut  90  to fasten square shaft  14  and coupling  60  together. When tightened, nut  90  and the head of bolt  88  bear against respective flats  69 . In use, axial compression loads applied to the assembly  58  are borne almost exclusively by shoulders  66  and  74 , minimizing axial stress on fastening bolts  84 ,  88 . 
       FIG. 17  depicts a helical soil pile assembly  98  that incorporates a coupling  100  according to a third embodiment of the invention. Coupling  100  joins a round shaft  12  to a round shaft  13 , to which at least one helical load-bearing plate  16  may be welded. Alternatively, shaft  13  may be an extension shaft devoid of load-bearing plates. As explained below, bolts  126 ,  130  secure the parts together. 
     Referring to  FIGS. 18-22 , coupling  100  comprises a hollow body  102  preferably formed as one piece, preferably of iron or steel. The body is symmetrical about two mutually orthogonal planes that intersect along its central longitudinal axis. The body has a cylindrical portion  104  that extends from one end of the body to a pair of diametrically opposed arcuate shoulders  106 , which extend laterally outward. The body also has a nose portion  108  that tapers inwardly. The taper facilitates soil penetration during installation, minimizing soil disturbance. Two diametrically opposed flats  109  on and adjacent nose portion  108  separate shoulders  106  from one another. A cylindrical socket  110  extends axially into body  102  through nose portion  108 , approximately up to the region of shoulders  106 . The cylindrical side wall  112  of socket  110  terminates in an inner end defined by an annular shoulder  114  that faces toward the open end of the socket. Two pairs of aligned transverse holes  116  extend through socket  110 , opening on flats  109 . A plurality (preferably two) pairs of aligned transverse holes  118  extend through cylindrical portion  104  remote from socket  110 . Preferably, holes  118  in cylindrical portion  104  are wider than holes  116  in nose portion  108  so as to accommodate wider bolts. 
       FIGS. 23 and 24  illustrate how coupling  100  is joined to two round shafts  12  and  13 . Cylindrical portion  104  is sized to fit closely within round shaft  12 , with the end  120  of shaft  12  abutting shoulders  106 . Shaft  12  has two pairs of aligned transverse holes  122 . Socket  110  is sized to closely receive shaft  13 , with the end of shaft  13  abutting annular shoulder  114 . Shaft  13  has two pairs of aligned transverse holes  124  near its end. When the three parts are assembled, holes  122  in shaft  12  align with holes  118  in body  102 . A bolt  126  placed through each of these two sets of aligned holes is secured by a nut  128  to fasten shaft  12  and coupling  100  together. In addition, holes  124  in shaft  13  align with transverse holes  116  through socket  110 . A bolt  130  placed through each of these two sets of aligned holes is secured by a nut  132  to fasten shaft  13  and coupling  100  together. When tightened, nuts  132  and the heads of bolts  130  bear against respective flats  109 . In use, axial compression loads applied to the assembly  98  are borne almost exclusively by shoulders  106  and  114 , minimizing axial stress on fastening bolts  126 ,  130 . 
     While various embodiments and have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications may be made. For example, any of the couplings described above can be provided with a differently configured socket: the couplings of  FIGS. 1 and 8  could be provided with a cylindrical socket to accommodate a round shaft; and the coupling of  FIG. 17  could be provided with a square socket to accommodate a square shaft. Alternatively, the sockets in these couplings could be configured to accommodate shafts that are neither square nor round. Other modifications may be made without departing from the scope of the invention as defined by the appended claims.