Abstract:
A circular concrete cap foundation poured in-situ within a perimeter forming corrugated metal pipe set atop or within an excavated pit and enclosing a series of circumferentially spaced pile anchors. The circular concrete cap foundation supports sets of inner and outer circumferentially spaced tower anchor bolts having their lower ends anchored to an embedded anchor ring and their upper ends projecting vertically and upwardly out the top of the circular foundation to engage the base flange of a supported tower. The pile anchors are formed with perimeter corrugated metal pipes set deep in subsurface soils with cementitious material surrounding and partially bonding to a centralized steel bolt or tendon which extends through the cap foundation. The tower anchor bolts and the pile anchor bolts are both partially encased in a PVC sleeve so that the bolts can be post-tensioned. The pile anchors are in tension only and serve to pull the cap foundation down to compress the underlying ground soils.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to concrete support foundations constructed in-situ particularly useful for supporting tall, heavy and/or large towers which may be used to support wind turbines, power lines, street lighting and signals, bridge supports, commercial signs, freeway signs, ski lifts and the like. More specifically, the pile anchor foundation of the present invention is useful in supporting such towers in clay or other fine grain soils which are water bearing and/or too weak to stand or maintain the dimensions of an excavation formed to receive a concrete foundation. Such soils can be found in the midwest region of the United States. 
     2. Description of Related Art 
     My earlier U.S. Pat. Nos. 5,586,417 and 5,826,387, entitled Tensionless Pier Foundation and Pier Foundation under High Unit Compression, respectively, and my pending U.S. patent application Ser. No. 10/067,999, filed Feb. 8, 2002 and entitled Perimeter Weighted Foundation for Wind Turbines and the like which is a continuation of U.S. patent application Ser. No. 09/671,282, now abandoned, disclose post-tensioned concrete tower foundations, the disclosures of which are incorporated herein by reference as if fully set forth. The prior art cited in these patents and application may also be relevant to the pile anchor foundation of this invention. 
     SUMMARY OF THE INVENTION 
     The foundation of this invention resists supported structure overturn by a multitude of circumferentially spaced post tensioned pile anchors. Each of the pile anchors includes a corrugated metal pipe (CMP) driven into subsurface soils. The CMPs are filled with cementious material securing a centralized bolt or tendon to be post-tensioned from a top surface of a concrete cap positioned above the pile anchors. The pile anchor bolts or tendons are encased, preferably in a plastic sleeve or the like, so that they do not bond to or bear into the upper foundation concrete cap, thus allowing the pile anchor to pull upward until skin friction resistance with the surrounding soils equaling the required tendon tension is achieved. The required bolt or tendon tension exceeds the maximum structure uplift load determined for each pile anchor. The pile anchors of this invention also differ from normal piles in that they are tension piles resisting only overturn uplift, and they do not serve as load bearing compression piles for supporting the structure. 
     In a conventional pile foundation, the piles extend upwardly through or into an overlying concrete foundation and are both compression and tension resisting foundation extensions. The piles in such foundations are not post-tensioned. The foundation of this invention allows pole and tower structure foundations to be constructed at or below ground surface in weaker water bearing soils susceptible to side wall caving when excavated. 
     The pile anchor foundation of the instant invention has a circular concrete cap set at or below ground surface which supports a tower from the upper surface thereof. The tower is attached to the concrete cap by a series of circumferentially spaced tower anchor bolts. The tower anchor bolts extend through and are nutted atop a circular tower base flange at the bottom of the tower and below an embedment ring near the bottom of the concrete cap. The tower anchor bolts are also sleeved and shielded so as to prevent the concrete from bonding to the anchor bolts. This structure allows the tower anchor bolts to be elongated and post-stressed between the tower base flange and the embedment ring to alleviate bolt cycling and fatigue. 
     The tower base flange is set in grout inside a grout trough molded by a template bottom ring. Leveling nuts are threaded onto several tower anchor bolts spaced around and underneath the tower base flange in a blockout void formed by blackouts of foam plastic or the like. The leveling nuts allow the tower to be plumbed vertically and support the base section of the tower while grout is poured into the grout trough under the tower base flange and cured. 
     Electrical and communication conduits are positioned in and through the concrete cap to allow wiring and conductors to be pulled into the tower. Also, reinforcement rebars are provided at the top and bottom of the concrete cap as well as lapping vertically near the perimeter thereof which are tied and placed radially between the anchor bolts. The rebar reinforcement is intended to resist bending forces in the concrete cap. 
     The pile anchor tendons or bolts, preferably in plastic sleeves or the like, and most preferably in PVC tubes, extend through the concrete cap and a pile anchor base plate, and into a major extent of the pile anchor cementitious material. The upper end of the tendon or bolt is equipped with a post-tensioning nut threaded thereon to post-tension the pile anchor and the concrete cap after the cementitious material thereof has hardened. 
     The pile anchors are constructed to terminate below the foundation concrete cap to form a gap which is preferably filled with a compressible material immediately below the foundation cap. The pile anchors around the perimeter are driven lengths of galvanized CMP filled with cementitious material except for the top of the CMP immediately below the bottom of the concrete cap. The cementitious material encases a centralized anchor bolt or tendon sleeved at the top and bare at its bottom with an end nut to facilitate the bottom of the bolt bonding with the cementitious material. 
     In accordance with the foregoing, it is an object of the present invention to provide a concrete foundation for supporting tall, heavy and/or large towers and/or poles which can be constructed in situ and is especially useful for supporting such towers in clay or other fine grain soils which are water bearing or otherwise too weak to stand or maintain the dimensions of an excavation formed to receive a concrete foundation. 
     A further object of the present invention is to provide a concrete foundation which includes a generally circular or cylindrical foundation cap set at or below the ground surface to support a tower from the upper surface thereof and a plurality of circumferentially spaced post tensioned pile anchors which depend a substantial distance into the ground below the base of the foundation cap. 
     Another object of the present invention is to provide a concrete supporting foundation in accordance with the preceding object in which each pile anchor includes an elongated bolt or tendon extending substantially throughout the length of the pile anchor, through the concrete cap and above the top surface thereof, for post tensioning the pile anchors and pull the concrete foundation cap downwardly to compress the underlying bearing soils. 
     Still a further object of the present invention is to provide the aforementioned bolts or tendons of the pile anchors with plastic sleeves or the like over a major portion of their upper extent to prevent bonding with the concrete in the upper portion of the pile anchor and the concrete cap, facilitate the post tensioning of the pile anchors and eliminate stress reversals and fatigue while the bolts are stretched by jacking or torquing during the post tensioning. 
     Yet another object of the present invention is to provide a concrete supporting foundation for large and heavy tower structures including a concrete foundation cap and downwardly extending pile anchors which are tension members only and serve to pull the concrete foundation cap downwardly to compress the underlying soils with such a compression force that the concrete foundation cap is always bearing on the underlying soils even under the greatest overturning and uplift forces transmitted to the foundation by the supported structure. 
     Other objects and advantages of this invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein is set forth by way of illustration and example, embodiments of this invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view, partially in section, of the completed cap and pile anchor foundation constructed in accordance with a preferred embodiment of the present invention. 
         FIG. 2  is a sectional view of the completed foundation with the tower base section flange set in the grout trough, with the concrete cap and pile anchors in accordance with preferred embodiments. 
         FIG. 3  is a top plan view of the foundation under the template, prior to concrete being poured. 
         FIG. 4  is an enlarged fragmental view, partly in section, of the completed foundation illustrating the upper pile anchor, the tower anchor bolts and foundation cap with the tower base flange positioned atop the foundation. 
         FIG. 5  is an enlarged fragmentary sectional view of the embedment ring at the bottom of the tower anchor bolts illustrating two nuts, PVC sleeve and a splice plate for connecting segments of the embedment ring. 
         FIG. 6  is an enlarged fragmental view illustrating the top of a post tensioned pile anchor with the compressible material filling the skin friction development gap between the top of the cementitious material of the pile anchor and the bottom of the foundation cap. 
         FIG. 7  is an enlarged fragmental view illustrating the bottom of the pile anchor with terminating nut and centralizer. 
         FIG. 8  is an enlarged fragmental view illustrating the template assembly. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although one preferred embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its scope to the details of construction and arrangement of components of this specific embodiment. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the preferred embodiment, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     Referring to the drawings, especially  FIGS. 1 and 2 , the foundation of the present invention is generally designated by reference numeral  52 . The foundation  52  of the present invention includes a circular or cylindrical foundation cap generally designated by reference numeral  46  and a series of circumferentially spaced pile anchor assemblies generally designated by reference numeral  47 . The foundation cap  46  preferably includes an outer upstanding corrugated metal pipe (CMP)  20  at its perimeter which may, for example, be 24 feet in diameter and 4 feet in height. The outer CMP  20  is placed atop the ground or in an excavation  29  formed in the ground and resting upon the bottom of the excavation  29 . (See  FIGS. 2 and 4 ). 
     Referring to  FIG. 2 , the void between the outer corrugated metal pipe  20  at the foundation cap perimeter and the edge of the excavation is filled with clean sand or sand cement slurry  30 . The foundation cap  46  includes a series of tower anchor bolts  13  spaced circumferentially about the central point of the foundation cap  46  (see  FIGS. 2 and 3 ). The tower anchor bolts  13  may be positioned in radial pairs forming two anchor bolt circles. The inner tower anchor bolt circle has a slightly shorter diameter than the outer tower anchor bolt circle. For example, the outer tower anchor bolt circle diameter may be 14 feet and the inner tower anchor bolt circle diameter may be 13 feet. The anchor bolts  13  are sleeved, preferably with PVC tubes  18 , which cover the anchor bolts  13  except for threaded portions at the top and bottom of the bolts (see  FIGS. 2  and  5 ). The anchor bolt sleeves  18  prevent bonding of the bolts  13  to the concrete and grout. 
     Referring to  FIGS. 2 and 5 , the lower ends of the tower anchor bolts  13  are anchored near the bottom of the concrete cap foundation  46  with an embedment ring  19  which preferably may be constructed of several circumferential segments lap jointed at  45 . The embedment ring  19  is preferably about the same size as and complementary to the tower base flange  33 . The ring  19  contains bolt holes for each of the anchor bolts  13 . The bolts  13  are secured in the bolt holes by any suitable securement, such as hex nuts  44  below the embedment ring  19  and hex nuts  43  atop the embedment ring as shown in  FIG. 5 . 
     Referring to  FIGS. 2 ,  3 , and  4 , reinforcing steel rebar  34  is positioned radially between the pairs of anchor bolts  13  and the pile anchor bolts  16 . The radial steel rebar  34  preferably are placed both near the top and bottom of the concrete cap foundation  46  and are lapped vertically and wire tied near and parallel to the outer CMP  20 . 
       FIGS. 1 and 2  show complete views of the pile anchor assemblies  47 . Each pile anchor assembly  47  consists of a pipe, preferably a corrugated metal pipe (CMP)  23 , driven into the ground sands, silts, clays, or combinations thereof by a mandrel pile driver. Post-tensioning pile anchor bolts or tendons, preferably all-thread bolts  16  with a nut  22  at the bottom, are centralized in the center of the pile anchor CMP  23  by pile anchor centralizers  32  (see  FIGS. 2 and 7 ). The pile anchor bolts  16  are sleeved, preferably by PVC tubing along a major upper portion  21  of their length to prevent bonding with the concrete foundation cap  46  and pile anchor grout  24  and to allow for post-tension stretching. The portion of the pile anchor bolts  16  below the PVC no bond zone and the bottom nut  22  are encased and secured in position by cementitious grout or concrete  24  pumped to fill the interior of the pile anchor CMP  23 . The grout or concrete  24  fills the interior of the pile anchor CMP  23  to within about two (2) feet of the bottom of the concrete foundation cap  46 , leaving an unfilled spaced  31  (see  FIG. 6 ). Following concrete pour and cure of the foundation cap  46 , the pile anchor base plates  17  are installed over the pile anchor bolts  16  atop the concrete foundation cap, and the post-tensioning nuts  28  are torqued or threaded snugly against the pile anchor plates  17  during the post-tensioning jacking of the pile anchor bolts  16  (see  FIG. 4 ). 
     Referring to  FIGS. 1 and 8 , the template assembly is generally designated by reference numeral  37 . The template assembly  37  is a temporary structure securing and positioning the anchor bolts  13  and Styrofoam blockouts  12  while forming a recessed tower grout trough  14  during pouring of the concrete for the foundation cap  46  and until the concrete initially sets. 
     The template assembly  37  consists of a generally square frame structure  50  comprising channels or I-beams  1  and  4  welded or bolted together. The frame structure  50  supports the top ring  7  and bottom ring  9  steel template rings unified and separated by several pieces of angle iron  8  which are welded between the steel template rings  7  and  9 . The template rings  7  and  9  have bolt holes in exact vertical alignment to match with the bolt holes in the tower base flange  33 . The steel template rings  7  and  9  are suspended below the frame structure  50  by all thread bolts  3  nutted atop the channels or I-beams  1  or  4  by nuts  38  and connected to the top template ring  7  by nuts  39  welded thereto. The nuts  38  can be turned to lengthen or shorten the space between the frame structure  50  and the top of the unified template rings  7  and  9  to allow the unified template rings to be leveled. The frame structure  50  is supported around the perimeter of the excavation  29  by any suitable support structure, such as wooden timbers  5  atop the surrounding ground. The wooden timbers  5  are stacked atop each other to the required height so the template assembly  37  is near level when placed atop the wooden timbers  5  by using a crane. 
     The blackouts  12  of “Styrofoam” or the like are duct taped underneath the bottom template ring  9  in at least three (3) positions to create voids in the concrete below the bottom of the grout trough  14 . These voids allow placement of the tower leveling nuts  11  which support the tower underneath the tower base flange and above the bottom of the grout trough  14 . The tower leveling nuts  11  are adjusted by turning in order to plumb the tower to a true vertical position prior to grouting the tower base flange  33  in position. The voids below the grout trough  14  created by the blockouts  12  also provide a space for lowering the leveling nuts  11  after the tower base flange  33  has been grouted into position and the grout has hardened sufficiently to support the tower. Lowering the leveling nuts into their respective blockout void provides a space between the top of the leveling nuts  11  turned down into the blockout void and the underneath side of the base flange  33 . This space allows those anchor bolts  13  with the leveling nuts  11  to be elongated by post-tensioning in the same manner as all other anchor bolts  13 . 
     Construction Sequence and Special Features 
     
         
         1. Drive pile anchor CMPs  23  with mandrel pile driver (not shown). The CMPs  23  will initially extend above the ground surface. 
         2. The pile anchor bolts or tendons  16  with PVC sleeves  18  and centralizers  32  are placed inside the CMPs  23 . 
         3. The pile anchor bolts or tendons  16  are grouted in place by pumping grout or concrete  24  into the pile anchor CMPs  23 . The top of the grout  24  should be at least two (2) feet below the bottom of the concrete foundation cap to be constructed, leaving gap  31 . 
         4. The grout  24  of pile anchors  47  is allowed to cure a minimum of twelve (12) hours before excavation (if required) for concrete foundation cap  46 . 
         5. Excavate for concrete foundation cap  46 . Hand work required around pile anchor CMPs  23 . 
         6. Place outer CMP  29  in excavation. 
         7. Cut off pile anchor CMPs  23  at bottom of concrete foundation cap and fill the two (2) feet of each pile anchor CMP with foam or other equivalent compressive filler. 
         8. Place bolts  13  with thread nuts  43  through holes in segments in embedment ring  19  and thread nuts  44  under embedment ring; install lap joints connecting embedment ring segments. 
         9. Place reinforcing rebars  34  top and bottom, tie wire rebar to anchor bolts and circular hoops near ends and bend. 
         10. Pour concrete and finish concrete foundation cap  46 . 
         11. Post-tension pile anchor bolts  16 . 
         12. Pour sand/cement slurry in annular space  30  between the concrete foundation cap  46  and edge of foundation. 
         13. After seven (7) days, install tower atop concrete foundation cap  46  and post-tension tower anchor bolts  13 . 
       
    
     The pile anchor foundation  52  of the present invention provides significant structural and operational advantages as follows:
         1. The pile anchors  47  of the pile anchor foundation  52  are tension members only which pull the concrete foundation cap  46  downward compressing the underlying bearing soils with such a compression force that the concrete foundation cap is always bearing on the underlying soils even under the greatest overturning and uplift forces transferred to the concrete foundation cap from the tower structure by the tower anchor bolts  13  atop the foundation cap.   2. The pile anchor bolts or tendons  16  are sleeved to eliminate stress reversals and fatigue while the bolt is stretched by jacking or torquing (post-tensioning).   3. The post-tensioned pile anchor bolts  16  are shielded from bonding with the reinforced concrete of the concrete foundation cap  46  allowing the bolts or tendons  16  to elongate when pulled upward by jacks to the required post-tension. The post-tensioned bolts or tendons  16  are secured in tension by nuts  28  which are threaded atop the pile anchor base plates  17  against the top of the concrete foundation cap  46 , thus pulling the cap  46  downward with great compression against the underlying soils. Pile anchor bolts or tendons  16  may be re-tensioned as necessary using thread nuts  28 .   4. The pull down/hold down force of the pile anchors  47  results from the post-tensioning of the pile anchor bolts  16  against the pile anchor base plates  17  atop the concrete foundation cap  46 . Each pile anchor  47  is pulled upwardly toward the bottom of the concrete foundation cap  46  until the resisting skin friction along the sides of the CMP  23  equals the post-tension of the tension bolt  16  centered in the CMP and restrained by the grout  24 . The post-tension downward force atop the concrete foundation cap  46  by each pile anchor  47  should exceed the determined maximum uplift of the pile anchor by a factor of 1.5 or greater.   5. The pile anchors  47  include compressible voids or foam filled spaces  31  between the bottom of the concrete foundation cap  46  and the top of the grout filled pile. The compressible space  31  allows the concrete cap foundation  46  to be pulled downward compressing and consolidating the underlying soils to the required bearing strengths and allowing the pile anchors  47  to pull upward developing the skin friction resistance equal to the pile anchor bolt or tendon post-tension.   6. The pile anchors  47  preferably have corrugated metal pipes  23  around their perimeter to maximize the skin friction resistance with the contacting exterior soils.   7. The pile anchor bolts or tendons  16  are preferably fitted with centralizers  32  to maintain their position in the center of the corrugated metal pipe  23 .   8. The pile anchors  47  are filled with cementitious grout or concrete to bond and secure all-thread bolts or tendons  16  as a structural unit with the perimeter corrugated metal pipe  23 .       

     The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.