Abstract:
A perimeter pile anchor foundation is built by forming a plurality of individual perimeter pile anchors in a large generally circular pattern to form a perimeter wall. The individual pile anchors are contiguous, each pile overlapping the adjacent piles on either side. The overlapping pile anchors form an arch such that compression and friction between the pile anchors resist soil caving and sloughing pressure when soil inside the perimeter wall is excavated, enabling the perimeter pile foundation to be effectively constructed in weak saturated soils and/or cohesionless sands that will not allow conventional concrete foundation excavations. A concrete foundation ring is formed inside the pile perimeter wall to support a tall and/or heavy tower or other structure subject to high upset forces.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to the field of pile anchor foundations for supporting tall, heavy and/or large towers or the like which can be subject to high upset forces. More particularly, the present invention is directed to a perimeter pile anchor foundation including a plurality of pile anchors drilled in a circular or generally circular pattern so that adjacent piles overlap and form an arch with compression between the piles to resist soil caving in weak soils. 
     2. Description of the Related Art 
     In known pile anchor foundations, the piles extend downwardly from a foundation cap into the underlying soil and are spaced from one another. Such foundations are limited by soil conditions, as weak or wet soils will cave or sluff when, during construction, the ground under the center of the cap is excavated vertically. 
     Various forms of concrete foundations utilizing operational features of the instant invention have heretofore been disclosed in my earlier U.S. Pat. Nos. 5,586,417, 7,707,797 and 7,618,217 (“the &#39;217 patent”), the disclosures of which are expressly incorporated herein in this application by reference as if fully set forth in their entirety. However, a need exists for a large deep concrete foundation capable of being constructed in cohesionless sands and weak soils with shallow ground water. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention is directed to a perimeter pile anchor foundation for supporting tower or other structures which may be subject to high upset forces. The foundation is built by drilling a plurality of individual perimeter pile anchors, or “piles”, in a large circular or generally circular pattern. The individual piles are contiguous, each pile overlapping the adjacent piles on either side. 
     To construct the overlapping piles, the piles are divided into odd and even piles which alternate with one another around the perimeter of the foundation. Either the odd or the even piles may be constructed first. For purposes of this description, the odd piles are selected for forming first. The odd piles are formed by drilling a vertical hole for each pile, filling the hole with concrete, and inserting a centralized bolt vertically in the concrete (the order of the last two steps could be reversed). (The centralized bolts may later be post-tensioned, although post-tensioning is not necessary for the pile anchor bolts.) The concrete in the odd piles is then allowed to preset to a limited degree. 
     The even piles are arranged in between the odd piles. Therefore, after the concrete of the odd piles has preset, adjacent vertical holes are then drilled. Since the holes overlap to some extent, the concrete of the odd piles is shaved as the auger forms the hole for the even piles. The holes for the even piles are then filled with concrete and provided with vertically oriented centralized bolts in the same manner as with the odd piles. 
     In one preferred embodiment, the even and odd piles are offset from one another so that the diameter of the circle formed by the even piles is different from the diameter of the circle formed by the odd piles. This offset is typically in the range of one quarter to one half of the pile diameter. As a result, the total perimeter formed by the odd and even piles together is not a perfect circle. 
     Once the perimeter piles have been formed with the concrete fully set, an annular steel plate formed as a ring having holes therein is then placed on top of the perimeter piles. The centralized pile bolts extend through the holes and are secured with nuts to retain bolt tension. Alternatively, the ring may be formed by a plurality of individual steel plates, one for each pile. Individual steel plates provide for greater flexibility with respect to the adjoining relationship of the piles and the centralized pile bolts. 
     The perimeter piles form a perimeter wall to stabilize and retain the soil outside the wall. The soil inside the perimeter wall can then be safely excavated to form the large deep concrete foundation with the perimeter wall, without the soil caving or sloughing into the excavation. 
     An annular steel plate formed as a ring having holes therein is then placed on top of the perimeter piles. The centralized pile bolts extend through the holes and are secured with nuts to retain bolt tension. Alternatively, the ring may be formed by a plurality of individual steel plates, one for each pile. Individual steel plates provide for greater flexibility with respect to the adjoining relationship of the piles and the centralized pile bolts. 
     According to a first embodiment, a first corrugated metal pipe (CMP), also referred to herein as the outer CMP, is placed vertically in the excavation inside the perimeter wall formed by the contiguous piles leaving an outer annular space between the inside of the perimeter wall and the outside of the outer CMP. A foundation bolt cage, including a plurality of vertically oriented sleeved tower anchor bolts and a horizontally oriented embedment ring, is installed vertically inside the first CMP with the embedment ring at the bottom. According to a first configuration of the first embodiment, the tower anchor bolts are arranged in two concentric circles. In a second configuration of the first embodiment, the bolts are arranged in a single bolt circle. The tower anchor bolts, whether arranged in a single circle or in two concentric circles, are nutted above and below the embedment ring to secure the embedment ring in place near the bottom of the tower anchor bolts and concrete foundation to be formed. A second CMP, also referred to herein as the inner CMP, and smaller in diameter than the first CMP, is installed vertically inside the tower anchor bolts and the embedment ring. This creates an inner annular space between the outer and inner CMPs through which the tower anchor bolts extend vertically. 
     A concrete plug is then poured in the bottom of the inner CMP, after which the area inside the inner CMP atop the plug is backfilled with soil to approximately five feet below the surrounding ground surface. Electrical, communication, and grounding conduits are installed through the first and second CMPs, the tower anchor bolts, and the perimeter piles, and then backfilling of the inner CMP is completed to within a minimum of about six inches from the top of the inner CMP for the concrete floor  61 . The inner annular space between the outer and inner CMPs through which the tower anchor bolts extend vertically is filled to within about three to four inches from the top of the CMPs to create a grout trough. The outer annular space between the inside of the perimeter wall and the outer CMP, and the floor  61  inside the inner CMP, are then filled with concrete. Once the concrete cures, shims are stacked as necessary to support level the tower base section for grouting, the three to four inch grout trough filled with grout, and the tower base section flange set over the tower anchor bolts on top of the shims and nutted at the top against the upper surface of the tower base flange so that the tower anchor bolts can be post-tensioned when connecting and securing the tower to the foundation. The embedment ring is locked into place near the bottom of the foundation by the nutted tower anchor bolts. 
     According to a second embodiment, after the perimeter piles are formed, only a single CMP, such as the inner CMP is vertically placed in the excavation inside the pile perimeter and spaced therefrom to create an annular ring between the CMP and the piles. A direct embedded section is suspended in position between the piles and the inner CMP. The direct embedded section includes a reinforcing steel cage formed by a loop of rebar having a generally U-shaped cross-section. The loop includes a piece of rebar bent to have a generally vertical inner leg and a generally vertical outer leg joined at the top by a generally horizontal length of the rebar. The bottom of each leg is secured in place with rebar spacing hoops that are wire tied to the leg. The direct embedded section also includes an extension with flanges at the top and bottom thereof. The extension extends above the top of the concrete poured in the annular ring and is used to connect the foundation to the tower to be supported thereon. The direct embedded section takes the place of the tower anchor bolts and embedment ring that are part of the first embodiment. 
     The remainder of the construction of the second embodiment of the foundation is essentially the same as that already described in connection with the first embodiment, including the pouring of a concrete floor or plug and partial backfilling inside the inner CMP, installation of electrical, communication, and grounding conduits, completion of the backfilling of the inner CMP, and pouring of concrete into the annular ring between the inside of the perimeter wall and the CMP. 
     When constructed according to either the first or the second embodiment, the ring of overlapping odd and even piles forms an arch between adjacent piles. Compression and friction between the adjacent piles resists soil caving and sloughing pressure when soil inside the generally circular perimeter of the piles is excavated. 
     Accordingly, one object of the present invention is to overcome the difficulties of constructing deep concrete foundations in weak soil and/or cohesionless sand which are subject to sloughing or caving in when excavated vertically by providing a perimeter pile foundation. 
     Another object of the present invention is to provide a perimeter pile foundation in accordance with the preceding object that is formed by drilling a plurality of individual pile holes in a large generally circular pattern and filling them with concrete to form a perimeter wall, with the individual piles being contiguous and each pile overlapping the adjacent piles on either side so that the overlapping piles form a continuous arch, with compression between the overlapping piles resisting soil caving and sloughing pressure when soil inside the circle of piles is excavated. 
     Another object of the present invention is to provide a perimeter pile foundation in accordance with the preceding objects in which a vertical bolt is placed into the concrete of each of the perimeter piles before the concrete stiffens, the bolts extending substantially throughout the length of the pile anchor from top to bottom and having centralizers at one or more intervals along the length of the bolts to keep each bolt in the middle of its respective pile. 
     Yet another object of the present invention is to provide a perimeter pile foundation in accordance with the preceding objects in which a circular steel ring is placed over the top of the piles, the ring having holes therein through which the pile bolts extend and are secured with nuts to retain bolt tension. 
     A further object of the present invention is to provide a perimeter pile foundation in accordance with the preceding objects in which a central annular ring or foundation ring of concrete is poured inside the circular pile perimeter, the central foundation ring being provided with structure connecting elements placed in the concrete before the concrete stiffens. 
     A still further object of the present invention is to provide a perimeter pile foundation in accordance with the preceding objects in which the central foundation ring of concrete is bounded on the outside by the perimeter piles and on the inside by a first corrugated metal pipe (CMP). 
     Yet another object of the present invention is to provide a perimeter pile foundation in accordance with the preceding objects in which the structure connecting elements include an embedment ring and a plurality of post-tensioned tower anchor bolts. 
     A further object of the present invention is to provide a perimeter pile foundation in accordance with the preceding two objects in which the foundation further includes a second CMP placed inside the first CMP creating an inner annular ring between the first inner CMP and the second outer CMP, with the tower anchor bolts extending through the inner annular ring which is filled with concrete to complete the tower anchor bolt installation, both the inner and outer CMPs being inside the perimeter piles. 
     Yet another object of the present invention is to provide a perimeter pile foundation in which the structure connecting elements include a direct embedded section including a reinforcing steel cage secured to a generally cylindrical embedded structure extension having a side wall with a flange at each of its upper and lower ends. 
     Yet still another object of the present invention is to provide a perimeter pile foundation in accordance with the preceding objects in which concrete is poured to fill the entire volume within the circular pile perimeter. 
     It is yet another object of the invention to provide a perimeter pile foundation that is not complex in structure and which can be constructed at low cost and is effective in weak saturated soils and/or cohesionless sand that will not allow conventional concrete foundation excavations due to sloughing and caving in of such soils. 
     These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a perimeter pile foundation having two tower bolt rings in accordance with a first embodiment of the present invention. 
         FIG. 1 a    is a top view of a circular arrangement of overlapping pile anchors in accordance with the perimeter pile foundation shown in  FIG. 1  with the odd and even piles offset from one another. 
         FIG. 2  is a sectional view of a second configuration of the first embodiment of the perimeter pile foundation having a single tower bolt ring in accordance with the present invention. 
         FIG. 3  is a side view of single pile anchor and bolt, like that shown in  FIG. 2 , in isolation and without centralizers. 
         FIG. 4  is an enlarged view of “Detail A” shown in  FIG. 3 . 
         FIG. 5  is an enlarged view of “Detail B” shown in  FIG. 3 . 
         FIG. 6  is a top view of a circular arrangement of overlapping pile anchors in accordance with the perimeter pile foundation shown in  FIG. 1 , in which the odd and even piles are not offset from one another. 
         FIG. 7  is a side view of the tops of three adjacent pile anchors with the bolts secured on overlapping individual steel plates. 
         FIG. 8  is a photograph showing a perspective view of five adjacent pile anchor bolts extending upwardly through individual steel plates that are not overlapping. 
         FIG. 9  is an enlarged top view of two overlapping piles as shown in  FIG. 6 . 
         FIG. 10  shows a sectional view of a second embodiment of the perimeter pile foundation in accordance with the present invention. 
         FIG. 11  is a perspective view of the extension of the direct embedded section shown in  FIG. 10 . 
         FIG. 12  shows a deep concrete perimeter pile anchor foundation in accordance with the present invention supporting a large tower. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing preferred embodiments of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     A first embodiment of a perimeter pile anchor foundation in accordance with the present invention is shown in  FIGS. 1, 1   a  and  2 . The perimeter pile anchor foundation, generally designated by reference numeral  10 , has a plurality of pile anchors or “piles”, each generally designated by the reference numeral  14  extending vertically downward into the soil  100  and forming a perimeter wall, generally designated by reference numeral  11 , for the foundation  10 . The pile anchors  14  thus serve to secure the concrete foundation  10  into the ground. A first or outer CMP  68  is placed vertically in the excavation inside the perimeter wall  11  to form an outer annular ring, generally designated by reference numeral  73 , between the inside of the perimeter wall  11  and the outer CMP  68 . 
     According to the first embodiment, a second or inner CMP  70  is placed inside the outer CMP  68 , forming an inner annular ring, also referred to herein as the foundation ring  72 . Extending through the concrete foundation ring  72  is a series of tower anchor bolts  18  spaced circumferentially in a circle about the central vertical axis of the foundation. The inner annular ring  72  is filled with concrete  12  either before or after placement of the tower anchor bolts. 
     The tower anchor bolts  18  can include two bolt circles as in the configuration shown in  FIGS. 1 and 1   a , or one bolt circle as in the configuration shown in  FIG. 2 . When using a one bolt circle, the bolts and the tower base flange  120  are inside the tower shell, a configuration known in the art as an L flange. With two bolt circles, generally designated by the reference numerals  20  and  22 , the bolt circles are positioned in radial pairs and can be used if the tower base flange  120  of the supported tower has a dual bolt circle, with one set of bolts being outside the tower shell  111  and one set of bolts inside the tower shell, resulting in a configuration known in the industry as a T flange. 
     The inner tower anchor bolt circle  20  has a slightly smaller diameter than the outer tower anchor bolt circle  22 . For example, the outer tower anchor bolt circle diameter may be about fourteen feet and the inner tower anchor bolt circle diameter may be about thirteen feet. A tower or other supported structure (not shown) can be attached to the concrete foundation by the tower anchor bolts  18 . Structures which can be supported on the perimeter pile anchor foundation of the present invention include, but are not limited to, transmission towers, electrical towers, communication towers, lighting standards, bridge supports, commercial signs, freeway signs, ski lift supports, solar energy towers, wind turbine towers, large stacks or chimneys, silos, tank structures, airport towers, guard towers, etc. 
     The tower anchor bolts  18  extend through and are nutted atop the circular tower base flange  120  at the bottom of the tower or other supported structure. The bottom ends of the bolts  18  extend to an embedment ring  32  near the bottom of the foundation. The embedment ring  32  contains bolt holes for receiving the bottom ends of each of the tower anchor bolts. The bolt ends are anchored to the ring with suitable nuts  102  and  103  or the like. The embedment ring  32  is preferably constructed of several circumferential segments lap jointed together. The embedment ring  32  is approximately the same size as and is complementary to the tower base flange  120 . 
     The tower anchor bolts  18  are sleeved in elongated hollow tubes, preferably PVC tubes, which cover the anchor bolts except for threaded portions at the top and bottom of the bolts. The anchor bolt sleeves prevent bonding of the bolts to the concrete  12  that is poured into the inner annular ring  72 . This sleeved structure allows the tower anchor bolts, with nuts  49 , to be elongated when post-stressed between the tower base flange  120  and the embedment ring  32  to alleviate bolt cycling and fatigue. A full description of the tower anchor bolts  18  is set forth in the &#39;217 patent, previously incorporated herein by reference. 
     As shown in  FIGS. 1 and 2 , the pile anchors  14  extend below the inner annular or concrete foundation ring  72 . Each pile anchor  14  includes an elongated bolt or tendon  36 , that extends through a pile anchor base plate  43  on the top surface of the foundation  10 , or preferably grouted into the top surface of the foundation, and then into a drilled pile hole  44  that is filled with pile anchor cementitious material to secure the pile anchors  14  in the ground or soil  100 . According to one embodiment, the concrete is a sand cement slurry, made with about 5 sacks of cement per cubic yard. The pile bolts  36  are on the order of 1.5 inches in diameter. Centralizers  50  are positioned at various intervals along the length of the bolts  36  to keep each bolt in the middle of its respective pile. 
     The embedded portion of each of the bolts  36  includes a lower end  38  that is bare, i.e., is in direct contact with the cementitious material, for bonding thereto when the cementitious material is poured or pumped to fill the interior of the drilled pile holes  44 . The cementitious material preferably fills the pile holes to their bottoms in soil  100 . An end nut  42  may be provided on the lower end of the bolt  36  to facilitate bonding of the bolt lower portion  38  with the cementitious material (see  FIGS. 1, 2 and 5 ). 
     If the pile bolts  36  are to be post-tensioned, the upper end of the embedded portion of the pile bolt  36  is encased in an elongated hollow tube (not shown), preferably in a plastic sleeve or the like, and most preferably by PVC tubing, to prevent bonding with the pile anchor cementitious material and to allow for post-tension stretching. This sleeved structure is fully disclosed in the &#39;217 patent, previously incorporated by reference herein. However, according to the present invention, the pile bolts  36  do not have to be post-tensioned, in which case the sleeve is not included, as is the case shown in  FIGS. 1, 2, 3 and 4 . 
     The perimeter pile foundation of the present invention is built by first drilling and then forming a plurality of individual perimeter pile anchors in a large generally circular pattern as shown in  FIGS. 1 a    and  6 . The pile anchors  14  are divided into a first group and a second group of piles, referred to herein as the odd and even piles, which alternate with one another around the perimeter of the foundation. The odd piles may be considered the first group or the second group, with the even piles therefore being designated whatever group the odd piles are not. 
     When forming the perimeter pile “circle”, the even and odd piles are preferably offset from one another so that the diameter of the circle formed by the even piles is different from the diameter of the circle formed by the odd piles as shown in  FIG. 1 a   . As a result, the overall perimeter formed by the odd and even piles together is not a perfect circle. Other generally circular configurations like that shown in  FIG. 6  are also possible. According to the offset embodiment shown in  FIG. 1 a   , the difference in the diameter of the odd and even bolt circles is approximately six inches. 
     The individual circular pile anchors  14  are approximately 18 inches in diameter, and together form a circular pattern that is about 21 feet in diameter. As shown in  FIGS. 1 a    and  6 , the individual pile anchors  14  are contiguous, each pile anchor having an overlap  60  with the adjacent pile anchors on either side. As shown in  FIG. 8 , the overlap  60  of the pile anchors  14  is between about one inch and about three inches. With this amount of overlap, the central bolts  36  in the pile anchors  14  that are about 18 inches in diameter are actually about 15 inches apart. 
     To construct the overlapping pile anchors  14 , either the odd piles or the even piles may be constructed first. For purposes of description, the odd pile anchors are formed first by drilling each odd pile hole  44 , filling the pile hole with concrete, and inserting a centralized bolt  36  vertically into the concrete to form the pile anchor  14 . The last two steps could be reversed. 
     The even piles are arranged in between the odd piles, with the concrete in the odd piles being allowed to preset to the stage where the concrete is firm but can still be shaved with the auger used to drill the even pile holes. The even pile holes are then drilled, filled with concrete and provided with vertically oriented centralized bolts as with the odd piles to form the even pile anchors  14 . The last two steps could be reversed. 
     The pile holes  44  and pile anchors  14  for the concrete foundation of the present invention can be formed in the soil below the excavation in a variety of ways and using differing equipment, depending upon the condition of the soil, as known to those skilled in the art. For example, the pile hole  44  may be simply formed by a driven mandrel or formed by a screw auger in generally stable soils. However, in unstable soils for which the perimeter pile anchor foundation of the instant application is particularly adaptable, the pile holes are preferably formed by driven pile pipes or pipes drilled, jetted or vibrated in place, such as in U.S. Pat. No. 7,533,505 which is co-owned by the applicant of this application, before positioning the pile anchor bolt, followed by the addition of the cementitious material. Alternately, the pile holes  44  may be drilled and the concrete pressure cast with hollow stemmed augers in wet sands and clays or the hole filled with the cementitious material through a tube which then serves as the anchor bolt. Other methods and equipment to form the pile anchors  14  known to those skilled in the art can be used without departing from the present invention. 
     Following completion and concrete set of the perimeter pile circle, the soils within the perimeter pile circle are excavated to the foundation depth  101 . As shown in  FIGS. 1 and 2 , the pile anchors may extend a few feet below the intended depth of the foundation to be constructed inside the circular pattern of perimeter pile anchors. This extension of the pile anchors is not necessary, however, as the pile hole depth may be substantially the same as the foundation depth  101 . 
     After the pile anchors have been formed, an annular steel plate  43  formed as a ring having holes therein is placed over the piles. The centralized pile bolts  36  extend through the holes and are secured with nuts  48  to retain bolt tension. Alternatively, the ring may be formed by a plurality of individual steel plates  45 , one for each pile, with adjoining steel plates that either overlap, as in  FIGS. 4, 6, 7 and 9 , or are spaced from one another as in  FIG. 8 . Having individual steel plates provides for greater flexibility with respect to the adjoining relationship of the piles and the centralized pile bolts. 
     The pile anchor base plate, whether formed as a ring  43  or as independent plates  45 , is preferably grouted into the top surface of the pile anchors  14 , forming the perimeter wall  11  of the foundation  10 . This can be readily accomplished by blocking out an indentation slightly larger than the dimensions of the base plate, such as by using a Styrofoam or other easily removable form. The use of block-outs is fully discussed in the &#39;217 patent, previously incorporated by reference. The pile anchor base plate(s) should be grouted into the top surface of the pile anchors so that the upper surface of the base plate coincides with the upper surface of the foundation  10 . 
     According to both configurations of the first embodiment, after the soils inside the perimeter wall  11  formed by the piles have been excavated to create area  76  as shown in  FIGS. 1 and 2 , the first or outer CMP  68  is placed vertically inside the perimeter wall  11  formed by the contiguous piles  14 . Placement of the outer CMP creates the outer annular space  73  between the inside of the perimeter piles and the outer CMP. A foundation bolt cage including a plurality of vertically oriented sleeved tower anchor bolts  18  and horizontally oriented embedment ring  32  is installed vertically inside the first CMP  68  with the embedment ring  32  at the bottom. The tower anchor bolts  18  can include two bolt circles in the configuration shown in  FIG. 1 , or one bolt circle in the configuration shown in  FIG. 2 . 
     The tower anchor bolts  18  are nutted at the bottom with the embedment ring  32  with nuts  102  and nutted atop the embedment ring with nuts  103  to secure the embedment ring in place near the bottom of the concrete foundation. The tower anchor bolts are used to secure the tower to the foundation as described in the &#39;217 patent, previously incorporated by reference herein. 
     The second or inner CMP  70 , having a smaller diameter than the first or outer CMP is then installed vertically inside the tower anchor bolts and the first CMP  68 . Placement of the second CMP creates the inner annular space defining the inner foundation ring  72  between the outer and inner CMPs through which the tower anchor bolts extend vertically. 
     A concrete plug  75  is then poured in the bottom of the inner CMP  70 , after which the area  76  inside the inner CMP atop the plug is backfilled with soil to approximately five feet below the surrounding ground surface. Alternatively, the entire area inside the inner CMP may be filled with concrete. Electrical, communication, and grounding conduits (not shown) are installed through the first and second CMPs  68 ,  70  and the perimeter pile anchors  14 , and then filling of the inner CMP  70  is completed with soil to within about six inches of the top of the inner CMP  70 . Once the backfill is completed, steel welded wire mesh (WWM) atop dobies (not shown) is placed on the backfill and a capped central drain (not shown) is installed and centered into the backfill. Dobies are typically 4″ by 4″ by 2″ concrete blocks with a tie wire cast therein which is used to secure the dobies to rebar. 
     The inner annular space or foundation ring  72  between the outer and inner CMPs is then filled with concrete to within about three or four inches of the of the top of the CMPs to create a grout trough  130  to complete the concrete foundation ring  72 . The six inch floor area and the outer annular space  73  between the outside of the outer CMP  68  and the inside of the perimeter wall is also filled with concrete. 
     According to a second embodiment shown in  FIG. 10 , after the pile anchors are formed, only an inner CMP  70  is vertically placed inside the pile perimeter and spaced therefrom to create an annular foundation ring  80  between the CMP  70  and the piles  14 . A direct embedded section, generally designated by reference numeral  85 , is placed near the top of the foundation ring  80 . The direct embedded section  85  includes a generally U-shaped reinforcing steel cage, generally designated by reference numeral  87 , formed by a loop of rebar coupled with a structure extension, generally designated by reference numeral  116 , which is shown in  FIG. 11 . The cage  87  is constituted by a piece of rebar bent to have a generally vertical inner leg  88  and a generally vertical outer leg  89  joined at the top by a generally horizontal length  90  of the rebar extending through holes  110  in the generally cylindrical side wall  112  of the extension  116  of the embedded section  85  to form the generally U-shaped configuration for cage  87 . Rebar spacing hoops  114  are wire tied near the end of each leg to secure the legs in place in a circular configuration. 
     The extension  116  of the direct embedded section  85 , shown as part of the foundation in  FIG. 10  and in isolation in  FIG. 11 , is separate from the rebar loops which extend through the holes  110  in the extension side wall  112 . The extension  116  has a flange  95  at the top and a flange  97  at the bottom. The embedded structure extension  116  is placed between the inner leg  88  and the outer leg  89  of the cage  87 , with the extension  116  extending above the top of the concrete poured in the foundation ring  80 . The top of the flange  95  is used to connect the foundation to the tower to be supported thereon. Hence, the direct embedded section  85  takes the place of the tower anchor bolts and embedment ring that are used in the first embodiment. 
     The remainder of the construction of the second embodiment of the foundation is the same as that already described in connection with the first embodiment, including the pouring of a concrete plug and partial backfilling inside the inner CMP, installation of electrical, communication, and grounding conduits, completion of the backfilling of the inner CMP, placement of the steel welded wire mesh (WWM) and the capped central drain, and pouring of concrete into the annular foundation ring  80  and the floor  61 . 
     When constructed, both embodiments of the perimeter pile foundation result in a ring of overlapping odd and even pile anchors that form a generally circular peripheral wall, each section of which is formed as an arch. As is known in the art, forces applied to an arch structure are all resolved into compressive stresses. This is useful when building the pile anchor foundation as described herein because building materials such as concrete can strongly resist compression. The horizontal compressive forces acting on the perimeter piles hold the piles against one another in a state of equilibrium. Thus, compression and friction between adjacent piles resist soil caving and sloughing pressure when soil inside the generally circular perimeter of the piles is excavated. The large deep concrete foundation may therefore effectively be used to support a large tower  160  or other structure like that shown in  FIG. 12 . 
     It should be understood by those skilled in the art that the foregoing description utilizes the terms “concrete” and “cementitious material” interchangeably. It will be further understood that various cementitious and cementitious-type materials can be utilized in constructing the post-tensioned pile anchor foundation of the present invention as would be utilized by those skilled in the art. These materials include, but are not limited to, sand-cement slurries, grout, and epoxy resins. 
     Further, while the elongated members in the pile anchors of the present invention have been described as bolts, those skilled in the art will appreciate that other elongated elements, such as strands, cables, rods, pipes, or the like, could be used in accordance with the present invention. 
     The foregoing descriptions and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not limited by the dimensions of the preferred embodiment. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.