Cementitious foundation cap with post-tensioned helical anchors and method of making the same

Abstract

A post-tensioned concrete cap foundation has helical anchors with pipes having several helical discs welded around the pipe perimeter to spin drill deep into subsurface soils or other soft materials with holes in the pipe for high pressure-grouting in place. The helical anchor pipes include a tensioning element for pulling and post-tensioning the helical anchor. The helical anchors are tension anchors which can be converted to compression anchors. The helical anchors in tension serve to pull the foundation cap down to compress the underlying soil while the compression anchors limit the maximum settlement of the concrete foundation cap. The foundation also includes perimeter-forming and interior corrugated metal pipes with upper and lower sleeved horizontally extending radial bolts that are secured to the pipes and post-tensioned to provide lateral foundation compression.

Claims

1. A method for forming a post-tensioned concrete foundation with helical anchors and a concrete foundation cap for supporting on its upper surface a structure subject to high upset and dynamic forces comprising the steps of: a) Preparing a ground surface for said foundation; b) Drilling a plurality of helical anchors to depth, each helical anchor including a helical anchor pipe that extends into the ground and a tensioning element atop said anchor pipe; c) Setting sleeves over said tensioning elements to enable post-tensioning of said helical anchors; d) Pouring a concrete/slurry leveling course encasing electrical, communication, and grounding trench with conduits if conduits are routed under the foundation; e) After concrete/slurry cures, pouring the concrete foundation cap with cementitious material; f) Allowing said cementitious material in said concrete foundation cap to cure and solidify around, without bonding to, said tensioning elements; and g) Post tensioning the helical anchors from above the concrete foundation cap using the tensioning elements.

2. The method of claim 1, further comprising, before the step of drilling, the step of coupling a plurality of linearly aligned hollow bars end to end with couplers to form a hollow bar helical anchor pipe, said hollow bar helical anchor pipe having helical discs and said couplers having grout holes formed therein.

3. The method of claim 2, further comprising the step of pressure grouting the hollow bar helical anchor pipes to force grout out through said grout holes and around said helical discs for ground improvement around the hollow bar helical anchor pipe and helical discs to improve the soil strength, increase the anchor size and improve the bond between the helical anchor pipe and the soil to increase the anchor pullout or downward load resistance thus increasing the foundation loading capacity and stiffness.

4. The method of claim 3, further including the step of isolating certain zones of the hollow bar helical anchor pipe for pumping measured grout quantities and pressure to specific zones using a packer.

5. The method of claim 1, further comprising the steps of: positioning corrugated pipes interior to and around a perimeter of said concrete foundation cap; and placing sleeved radial bolts or tendons horizontally across the foundation and securing the radial bolts to the corrugated pipes.

6. The method of claim 5, further comprising the step of tensioning the sleeved horizontally extending radial bolts or tendons from outside the perimeter corrugated metal pipe.

7. The method of claim 1, further comprising adding a steel plate topped with a compressible material below the foundation cap to provide compression anchor capabilities to some of the helical anchors to limit the maximum settlement of the concrete foundation cap, said compressible material allowing the concrete foundation cap to be pulled down so the steel plate contacts the bottom of the concrete foundation cap, limiting additional concrete foundation cap settlement.

8. The method of claim 1, further comprising the step of pressure grouting each of the helical anchor pipes through grout holes formed in the pipes.

9. A method for forming a post-tensioned concrete foundation with helical anchors and a concrete foundation cap for supporting on its upper surface a structure subject to high upset and dynamic forces comprising the steps of: drilling a plurality of helical anchors to depth in a ground surface, each helical anchor including a helical anchor pipe that extends into the ground and a tensioning element atop said anchor pipe; pouring the concrete foundation cap with cementitious material over the plurality of helical anchors, said tensioning elements extending upwardly through said concrete foundation cap; allowing said cementitious material in said concrete foundation cap to cure and solidify around, without bonding to, said tensioning elements; and post tensioning the helical anchors from above the concrete foundation cap using the tensioning elements.

10. The method of claim 9, further comprising the step of setting sleeves over said tensioning elements before said step of pouring the concrete foundation cap.

11. The method of claim 10, further comprising the step of coupling a plurality of linearly aligned hollow bars end to end with couplers to form a hollow bar helical anchor pipe, said hollow bar helical anchor pipe having helical discs and said couplers having grout holes formed therein.

12. The method of claim 11, further comprising, after the step of setting sleeves over said tensioning elements and before pouring the cap, the step of pressure grouting the hollow bar helical anchor pipes to force grout out through said grout holes and around said helical discs for ground improvement around the hollow bar helical anchor pipe and helical discs to improve the soil strength, increase the anchor size and improve the bond between the helical anchor pipe and the soil to increase the anchor pullout or downward load resistance thus increasing the foundation loading capacity and stiffness.

13. The method of claim 12, further including the step of isolating certain zones of the hollow bar helical anchor pipes and pumping grout in measured quantities and pressure to specific zones in said pipes using a packer.

14. The method of claim 11, further comprising, before the step of pouring the cap, the step of placing a steel plate topped with a compressible material on the hollow bar at or above ground level, the compressible material providing compression anchor capabilities to some of the helical anchors to limit the maximum settlement of the concrete foundation cap, said compressible material allowing the concrete foundation cap to be pulled down so the steel plate contacts the bottom of the concrete foundation cap, limiting additional concrete foundation cap settlement.

15. The method of claim 11, further comprising, after the step of pouring the cap, the step of pressure grouting the hollow bar helical anchor pipes to force grout out through said grout holes and around said helical discs for ground improvement around the hollow bar helical anchor pipe and helical discs to improve the soil strength, increase the anchor size and improve the bond between the helical anchor pipe and the soil to increase the anchor pullout or downward load resistance thus increasing the foundation loading capacity and stiffness.

16. The method of claim 15, further including the step of isolating certain zones of the hollow bar helical anchor pipes and pumping grout in measured quantities and pressure to specific zones in said pipes using a packer.

17. The method of claim 9, further comprising, before the step of pouring the cap, the steps of: positioning corrugated pipes interior to and around a perimeter of said concrete foundation cap; and placing radial bolts or tendons horizontally across the foundation and securing the radial bolts to the corrugated pipes.

18. The method of claim 17, further comprising the step of placing sleeves over said radial bolts or tendons before placing said radial bolts or tendons horizontally across the foundation.

19. The method of claim 18, wherein the step of post tensioning the helical anchors using the tensioning elements includes the step of tensioning the sleeved horizontally extending radial bolts or tendons from outside the perimeter corrugated metal pipe.

20. The method of claim 9, wherein the step of drilling includes the steps of: pressure grouting each of the helical anchor pipes through grout holes formed in the pipes; and attaching the tensioning elements to upper ends of the helical anchor pipes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects, features and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings. While intending to illustrate the invention, the drawings are not necessarily to scale.

(2) FIG. 1 is a perspective view, partially in section, of a completed concrete foundation with post-tensioned bolt helical anchors and foundation cap constructed in accordance with a first preferred embodiment of the present invention.

(3) FIG. 2A is a sectional view of the post-tensioned bolt helical anchor and foundation cap with the tower base section flange set in the grout trough, and showing the concrete foundation cap and two tension-only bolt helical anchors in accordance with the first preferred embodiment of the present invention.

(4) FIG. 2B is a sectional view of the post-tensioned bolt helical anchor and foundation cap with the tower base section flange set in the grout trough, and showing the concrete foundation cap, one tension-only bolt helical anchor and one convertible bolt helical anchor in accordance with the first preferred embodiment of the present invention.

(5) FIG. 3 is a top plan view of the foundation steel components under the template, prior to concrete being poured.

(6) FIG. 4 is an enlarged fragmental view, partly in section, of the completed foundation illustrating an upper end of a bolt helical anchor, the tower anchor bolts and the concrete foundation cap with the tower base flange positioned and grouted atop the foundation.

(7) 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.

(8) FIG. 6 is an enlarged fragmental view illustrating the top of two post-tensioned tower anchor bolts engaging the tower base flange with the grout filling the grout trough between the top of the concrete foundation cap and the bottom of the tower base flange.

(9) FIG. 6A is a side view of a vertically and horizontally post-tensioned concrete foundation supporting a tower in accordance with the present invention.

(10) FIG. 7 is a sectional view illustrating a tension-only bolt helical anchor according to the first embodiment with anchor bolts or anchor tendons as the post-tensioning elements, with the upper end extending through the concrete foundation cap and the helical anchor pipe at the lower end made up of coupled pipe sections with helical discs mounted exteriorly thereon.

(11) FIG. 8 is an enlarged fragmental view illustrating the upper end of the tension-only bolt helical anchor shown in FIG. 7 including a threaded anchor bolt, plated and nutted at the top and connected to the helical anchor pipe by a subassembly, all within a PVC sleeve.

(12) FIG. 8A is an enlarged side view of the subassembly in FIG. 8 which connects the anchor bolt or anchor tendon of the bolt helical anchor at its lower end to the upper end of the helical anchor pipe.

(13) FIG. 9 is a sectional view illustrating a bolt helical anchor configured as a convertible bolt helical anchor to provide both tension and load bearing compression, the upper end extending through the concrete foundation cap with a compression plate in the leveling course below the concrete foundation cap and above the helical anchor pipe.

(14) FIG. 10 is an enlarged fragmental view illustrating the convertible helical anchor shown in FIG. 9 with a compression apparatus including a steel plate topped by compressible material and supported below by a subassembly connecting the helical anchor bolt to the helical anchor pipe.

(15) FIG. 11 is an enlarged fragmental view of two lengths of the helical anchor pipe shown in FIG. 9 connected by a coupler and having spiral and inertia rough welds.

(16) FIG. 12 is an enlarged fragmental view of a helical disc positioned around the helical anchor pipe of the type shown in FIG. 9 with grouting holes and spiral welds around the pipe perimeter.

(17) FIG. 13 is a partial sectional view of the foundation cap showing a grounding configuration in accordance with the present invention.

(18) FIG. 14 is a side view of a bolt helical anchor of the type shown in FIG. 9 having a helical anchor pipe with grouting ports in accordance with the first embodiment of the present invention and illustrating a packer and grout pump used to pressure grout the anchor pipe positioned in the excavation or on the ground before the foundation cap is formed.

(19) FIG. 15 is a sectional view illustrating a tension-only hollow bar helical anchor according to a second embodiment of the present invention, with the upper end of the hollow bar helical anchor extending through the concrete foundation cap and the lower end including coupled pipe sections having helical discs mounted on the couplers.

(20) FIG. 16 is a sectional view illustrating a convertible hollow bar helical anchor assembly according to the second embodiment.

(21) FIG. 17 is a sectional view of a post-tensioned hollow bar helical anchor and foundation cap according to the second embodiment with two convertible hollow bar helical anchors, each having a compression apparatus including a steel plate topped by compressible material and supported below by the coupler at the upper end of the embedded hollow bar anchor pipes at or near ground level.

(22) FIG. 18 is an enlarged fragmental view of two lengths of hollow bar helical anchor pipes connected by an internally threaded coupler shown in cross section and having helical discs mounted thereon and grout holes therein in accordance with the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(23) Although preferred embodiments of the invention are 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.

(24) Referring to the drawings, FIGS. 1-12 illustrate the overall foundation and specific structures of post-tensioned helical anchors in accordance with a first embodiment of the present invention, i.e., the so-called “bolt helical anchors”. As shown in FIGS. 1, 2A and 2B, the foundation of the present invention is generally designated by reference numeral 52. The foundation 52 includes a post-tensioned circular or cylindrical concrete foundation cap, generally designated by reference numeral 46, and a series of circumferentially spaced, post-tensioned bolt helical anchors or helical anchor assemblies, generally designated by reference numeral 47.

(25) 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 5 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 and grout leveling course 1. Referring to FIGS. 2A and 2B, the void 2 between the outer corrugated metal pipe 20 at the concrete foundation cap 46 perimeter and the edge of the excavation 29 is backfilled with clean sand or a sand cement slurry 30.

(26) The concrete foundation cap 46 includes a series of tower anchor bolts 13, 14 spaced circumferentially about the central point of the concrete foundation cap 46 (see FIGS. 2A, 2B and 3). The tower anchor bolts 13, 14 are preferably positioned in radial pairs forming two anchor bolt circles. The inner circle of tower anchor bolts 13 has a slightly smaller diameter than the outer circle of tower anchor bolts 14. For example, the outer tower anchor bolt circle may have a diameter of 14 feet and the inner tower anchor bolt circle may have a diameter of 13 feet. The tower anchor bolts 13, 14 are sleeved, preferably with PVC tubes 18 or the like, which cover the anchor bolts 13, 14 except for threaded portions 39, 42 at the top and bottom of the bolts (see FIGS. 2A, 2B and 5). The anchor bolt sleeves 18, whether made of PVC or other material(s), prevent bonding of the bolts 13, 14 to the concrete and grout.

(27) Referring to FIGS. 2A, 2B, 5 and 6, the lower ends of the tower anchor bolts 13 are anchored near the bottom of the concrete foundation cap 46 with an embedment ring 19 which preferably may be constructed of several circular 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 32 for each of the anchor bolts 13, 14. The bolts 13, 14 are secured in the bolt holes 32 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.

(28) FIG. 6 shows the top of a post-tensioned foundation cap 46 with the upper ends of the tower anchor bolts 13 projecting through the tower base flange 33. Tower anchoring hex nuts 39 are threaded onto the tower anchor bolts and the tower 60 (see FIGS. 2A, 2B and 6) which extend upwardly well above the tower base flange. Grout 37, which is poured into the grout trough 41 before placement of the tower and tower base flange, extends under the tower base flange 33 to complete installation of the tower 60.

(29) FIGS. 1, 2A and 2B show complete views of the bolt helical anchor assemblies 47 with tensioning elements including elongated anchor bolts or anchor tendons according to the first embodiment. Each bolt helical anchor assembly 47 includes a helical anchor pipe 23 with helical discs 25 welded around its perimeter. The helical anchor pipes 23 are sectioned typically in 5 ft. to 20 ft. lengths. The helical anchor pipes 23 are bolted together with bolts or studs through bolted pipe couplers 8 as shown in FIG. 11. The helical discs around the perimeter of the pipe allow the helical anchor to be spin drilled deep into the ground which may include sands, silts, clays, weak rock or combinations thereof to depths of about 40 feet to about 100 feet, or more, as desired.

(30) Post-tensioning helical anchor bolts or tendons 3 are preferably threaded bolts with a nut 28 at the top. The helical anchor bolts 3 are preferably steel rods of grade 75 or 150 and have a diameter on the order of 1.75 inches. The size and grade of the rods may be varied depending upon the load requirements for the foundation.

(31) The helical anchor bolts 3 are connected at their lower end to the helical anchor pipe 23 by a subassembly 4 (see FIGS. 2A, 2B, 7, 8 and 8A). The subassembly 4, shown in an enlarged view of FIG. 8A, includes a pipe bolt coupler 64 having a blind bore 65 with inner threads 66 for threaded engagement with the lower end of the anchor bolt 3 of the helical anchor. The pipe bolt coupler 64 is preferably between about 4 inches and about 6 inches in length, with the internal threading extending approximately 75% of the length of the coupler. Preferably, the threaded portion of the anchor bolt is about 3 to 4 inches in length, or roughly twice the diameter of the anchor bolt 3. The pipe bolt coupler 64 is connected at its lower end, preferably by an inertia weld 68, to a rod 70 having holes 72 therein for receiving pipe bolts (not shown). The pipe bolts pass through the holes 72 and through corresponding aligned holes in the top of the anchor pipes 23 to secure the pipes to the subassembly 4.

(32) The helical anchor bolts 3 are sleeved, preferably by PVC tubing 5, through the concrete foundation cap 46 to prevent bonding with the concrete foundation cap 46 and to allow for post-tension stretching. As shown in FIGS. 7 and 8, the subassembly 4 and the top of the anchor pipe 23 are also within the sleeve 5. The portions 16 of the helical anchor pipes 23 below the PVC no-bond zone have drilled holes or grouting ports 48 as well as helical anchor discs 25 welded around the perimeter as shown in FIG. 12. The grouting ports 48 preferably have a diameter of about one-half inch and allow for pressure grouting of the anchor pipes 23 and their surrounding soils with measured quantities and pressures after the helical anchor assembly 47 is spin drilled deep into the ground.

(33) The perimeter surface of the helical anchor pipes 23 is preferably deformed by spiral and inertia welds 26 shown in FIGS. 8, 10, 11 and 12. The spiral and inertia welds 26 increase the strength of the bond between the pipes and the grout that is injected under pressure into the pipe and forced out through the grouting holes 48 in the pipe to surround the exterior of the pipe. The anchor pipe welds may be formed with an arc welder or by other means as would be known by persons of skill in the art.

(34) Pressure grouting of the anchor pipes 23 through the drill holes or grouting ports 48 in the anchor pipes 23 can include the use of a packer 102, as shown in FIG. 14. After the anchor pipes are spin drilled into the ground and before the foundation cap is formed, grout 24, preferably cement or a sand cement slurry material or the like, is injected by a grout pump 90 through a hose 92 and then to a grouting pipe 94 that is connected to the hose 92 and the pipe 23. The injected grout fills the pipe and exudes under injection pressure through the grouting ports 48, preferably positioned adjacent the helical discs 25. Having been forced through the grouting ports 48, the grout then surrounds the outside of the pipe 23 and the helical discs 25, increasing the helical disc bearing and skin friction resistance of the anchor pipe with surrounding soil.

(35) To grout the anchor pipes 23, the packer 102 is inserted into the hollow annulus 9 (see FIGS. 8 and 10) of the helical anchor pipe 23 and inflated to confine pressure-grouting to an area below the packer. The grouting pipe 94 passes through the packer 102 to provide pressurized grout to that portion of the pipe 23 below the packer. After intended quantities and pressures are reached in a lower zone of the helical anchor pipe 23, the packer 102 is deflated, moved upward and reinflated to pressure-grout the next zone above the previous zone. Packers that can be used with the present invention are available from Geopro S.A. of Belgium.

(36) More particularly, the packer 102 is first placed above the lowest grouting ports 48. Grout is injected until a specified pumping pressure is reached at which time the grout volume is recorded. The packer 102 is then moved upwardly above the next set of grouting ports and the pressurized grouting process is repeated. After all grouting ports have been grouted, the subassembly 4 is inserted into the helical anchor pipe 23 with the holes 72 in the rod 70 aligned with corresponding holes in the anchor pipe. Bolts are then inserted through the aligned holes and secured with nuts to securely connect the pipe 23 to the rod 70 of the subassembly 4.

(37) As shown in FIG. 13, grounding is provided by a mechanical cable 73 connected to the corrugated metal pipes (CMPs) at 74, 76 and 78, and to subassembly bolts at 82 and tower anchor bolts at 84. In addition, the cable 73 is connected by a copper grounding wire 86 to the tower base flange 33.

(38) While FIG. 2A shows two bolt helical anchors configured as tension-only members, some of the helical anchor assemblies 47 may be constructed as convertible helical anchors, generally designated by reference numeral 27, as shown at the right of FIG. 2B and in FIGS. 9 and 10. As noted earlier, the convertible helical anchors are configured to provide both tension and load bearing compression. While all of the helical anchors could be constructed as convertible helical anchors, generally approximately only 25% to 50% of the anchors are constructed to be convertible helical anchors 27. When providing for load bearing compression the convertible anchors serve to limit the maximum settlement of the concrete foundation cap 46.

(39) The convertible helical anchors 27 terminate with the subassembly 4 connection to the helical anchor bolts 3 below the leveling course 6 beneath the concrete foundation cap 46. As shown in FIGS. 9 and 10, compression plate 7 is set atop the subassembly 4 with a helical anchor compression disc 31 of Styrofoam or the like set atop the compression plate 7 and extending upward into the leveling course 6. Following concrete pour and cure of the concrete foundation cap 46, the helical anchor base plates 17 are installed over the threaded helical anchor bolts 3 atop the concrete foundation cap 46, and the post-tensioning nuts 28 are torqued or threaded snugly against the helical anchor plates 17 during the post-tensioning jacking of the helical anchor pipe bolts 3 (see FIGS. 2A, 2B, 7, 8 and 9). The convertible anchors act as tension members until the cap settles to reach the compression plate 7 at which point the compressible disc 31 allows the concrete cap foundation 46 to be pulled downwardly, compressing and consolidating the underlying soils to the required bearing strengths and allowing the helical anchors 47 to pull upwardly, developing skin friction resistance equal to the helical anchor pipe bolt or tendon 3 post-tension.

(40) Referring to FIGS. 2A, 2B, 3, and 4, radially extending bolts 34 are positioned horizontally between the pairs of anchor bolts 13, 14 and the helical anchor bolts 3. The radial bolts 34 preferably are placed near both the top and bottom of the concrete foundation cap 46. The radial bolts pass through internal corrugated metal pipes 21 and 22 which provide hoop and vertical steel reinforcement, as well as bolt support before the concrete foundation cap 46 pour is made. The horizontally extending radial bolts 34 are nutted 35 outside the perimeter-defining corrugated metal pipe 20 and inside the innermost corrugated metal pipe 22. While not shown, a plate is preferably positioned between the nut 35 and the outer surface of the corresponding pipe wall to reinforce the pipe wall and distribute the pressure created by the nut upon tightening thereof. The radial bolts 34, which are preferably sleeved, are post-tensioned from the perimeter of the concrete foundation cap 46 following pour and cure of the concrete foundation cap 46. The void 2 between the corrugated metal pipe 20 and the edge of the foundation excavation 29 is backfilled with clean sand or a sand cement slurry 30 after the horizontally extending radial bolts 34 are post-tensioned.

(41) The radial bolts 34 may be steel rods of grade 75 or less, and may alternatively be embodied as cables, known as strands. The strands are typically about 0.5 inches in diameter, with two to three of such strands being wrapped together depending on the strength needed. When strands are used, a sleeve of PVC or other material is not necessary as the strands are generally provided with a rubber sheath from the manufacturer. Nuts are not used to tighten the cables or strands, but rather a specialized tool known as a wedge that has teeth that bite into the cables as they are stretched during post-tensioning; such a tool is known to persons of skill in the art. A representative multistrand post-tensioning cable system is the DYWIDAG post-tensioning system available from DYWIDAG Systems International (DSI) having locations worldwide.

(42) The helical anchor bolts 3 used in a tension-only bolt helical anchor are generally between about 2 feet and about 5 feet in length, and preferably about 3 feet in length. The helical anchor bolts 3 used in a convertible bolt helical anchor are approximately 6-8 feet in length. The additional length is needed because the anchor bolts 3 need to extend all the way through the foundation cap.

(43) The second embodiment according to the present invention, i.e., the so-called “hollow bar helical anchor”, is shown in FIGS. 15-18. Many of the structural components of the second embodiment are the same as those already described in connection with the first embodiment. Accordingly, description of the components that are common to both embodiments will not be repeated here.

(44) FIG. 15 is a sectional view illustrating a tension-only hollow bar helical anchor, generally designated by reference numeral 187, according to the second embodiment. Each hollow bar helical anchor 187 is formed by coupling together lengths of externally threaded hollow bar pipes or anchor rods 184 which are typically sectioned in 5 foot to 20 foot lengths. As in the first embodiment, the lower part of the hollow bar helical anchor 187 includes a hollow bar helical anchor pipe 184 with helical discs 25 welded around the perimeter and grout ports 48 drilled through the couplers connecting lengths of externally threaded hollow bar pipes or anchor rods. For increased friction against the soil, the hollow bar helical anchor pipes 184 do not require spiral or inertia welds as they have exterior rolled threads 127 (3 threads to the inch) which are about ⅛ inch wide and a 16.sup.th of an inch high. Hollow bar pipes suitable for use in the second embodiment of the present invention include those manufactured and sold by the Williams Form Engineering Corporation of Belmont, Mich., as part of their Hollow All-Thread Self-Drilling Anchoring System.

(45) The upper portion of the hollow bar helical anchor 187 includes a short length of hollow bar 185 which serves as a tensioning element, with a sleeve 5 to prevent adhesion to cementitious material of the foundation cap 46. The sleeved length of hollow bar 5 extends through the foundation cap 46 and is post-tensioned on the upper surface of the cap by nuts 28 in the same manner as the anchor bolts 3 of the first embodiment.

(46) The desired number of pipes or hollow bars are assembled end-to-end with internally threaded bolted couplers 188, best shown in FIG. 18. The internally threaded couplers 188 are approximately 12 inches in length and connect the externally threaded ends of two linearly aligned hollow bar anchor pipes which are received within opposing ends of the coupler as shown in FIG. 18. Once assembled, the coupler 188 is bolted or affixed to each end of bars 184 by any suitable means. The short length of hollow bar 185 is coupled to the upper end of the embedded hollow bar 184 using a coupler 188 in the same manner as the embedded sections of hollow bar are coupled together.

(47) FIG. 16 is a sectional view illustrating a convertible hollow bar helical anchor assembly, generally designated by reference numeral 227, according to the second embodiment. Like the first embodiment, the convertible hollow bar helical anchor assembly 227 includes a compression apparatus with an anchor plate 7 topped by a compressible disc 31, with the hollow bar passing through openings in the anchor plate and disc. The short length 185 of hollow bar that extends through the cap is coupled to the upper end of the embedded hollow bar 184 using a coupler 188.

(48) FIG. 17 shows two convertible hollow bar helical anchors 227 as incorporated within the overall foundation of the present invention. As shown, the anchor plate 7 is supported by the underlying coupler 188 at the upper end of the embedded hollow bar 184 at or near ground level.

Construction Sequence and Special Features for First Embodiment

(49) 1. At the desired location, excavate the ground for constructing the circular concrete foundation cap to a depth which allows a minimum of 1 ft. of the circular concrete foundation cap to extend above building pad subgrade. Compact the bottom of the excavation 29.

(50) 2. Spin drill the desired number of bolt helical anchor assemblies 47 to the desired depth. The number of bolt helical anchor assemblies 47 typically depends upon the number of tower anchor bolts. Helical anchor pipes 23 are sectioned typically in 5 ft. to 20 ft. lengths and bolted together with bolts or studs through bolted couplers 8. The helical anchor discs 25 auger downward into the ground material.

(51) 3. Pressure-grout each bolt helical anchor 47 through grout holes or ports 48 in the anchor pipe 23. If desired, the grout can be placed sequentially from the bottom up using a packer 102 (see FIG. 14).

(52) 4. Allow the grout 24 of the bolt helical anchor to cure a minimum of twelve (12) hours before the subassemblies 4 are placed and used to attach the helical anchor pipe 23 to threaded helical anchor bolts 3.

(53) 5. Excavate a trench below the concrete foundation cap excavation 29 for electrical, communication, and grounding conduits 11 (see FIGS. 2A and 2B), if they are not routed through the concrete foundation cap 46.

(54) 6. Install and secure in place the electrical, communication, and grounding conduits (not shown) in trench 11 if under the concrete foundation cap 46. If the electrical, communication, and external grounding conduits are routed between the tower anchor bolts 13 and through the concrete foundation cap 46, place and secure the electrical, communication and external grounding conduits prior to pouring concrete for the concrete foundation cap 46. Place the compression plates 7 atop the subassemblies 4 of the convertible anchors, place the convertible bolt helical anchor compression discs 31 atop the compression anchor plates 7, and place helical anchor bolt PVC pipes 5 or the like atop the discs 31.

(55) 7. Place and secure the internal grounding wire 12 to the helical anchor pipes 23. Leave tails for later connection of the internal grounding wire (not shown) to the perimeter corrugated metal pipe 20, the internal corrugated metal pipes 21 and 22, and the supported structural tower base flange 33.

(56) 8. Pour the concrete/slurry leveling course 6 and the electrical, communication, and grounding trench 11 if the conduits are routed under the foundation.

(57) 9. Assemble the tower anchor bolt cage, generally designated by reference numeral 10 (see FIGS. 2A and 2B) which includes the template ring 15 (see FIG. 1), the embedment ring 19 along with the lap joints 45, tower anchor bolts 13, 14, the hex nut 43 above the embedment ring and the hex nut 44 below the embedment ring. Place, level, and secure the tower anchor bolt cage 10 centered in the concrete foundation cap 46 footprint.

(58) 10. Place the perimeter corrugated metal pipe 20 and the internal corrugated metal pipes 21 and 22. Drill holes 32 in the corrugated pipes for passing through the horizontally extending radial bolts 34 if the holes were not pre-drilled. Connect the internal grounding wire to the corrugated metal pipes 20, 21 and 22.

(59) 11. Insert the sleeved horizontal radial bolts 34 through the holes 32 in the corrugated metal pipes and between the sleeved tower anchor bolts 13, 14. Place nuts 35 on threaded ends beyond the bolt sleeves inside the innermost internal corrugated metal pipe 22 and outside the perimeter corrugated metal pipe 20.

(60) 12. Pour concrete and finish concrete foundation cap 46. Remove the template ring 15 for reuse a minimum of one (1) day after concrete cure.

(61) 13. After a minimum of three (3) days of concrete cure, or after concrete cylinder break tests determine a specified concrete strength, tension the horizontally extending radial bolts 34 from outside the perimeter corrugated metal pipe 20.

(62) 14. Place and level the helical anchor base plate 17 atop leveling shims (not shown) and a thin layer 40 of cementitious grout (see FIGS. 2A, 2B and 8). After grout cure of a minimum of one (1) day, post-tension the bolt helical anchor assemblies 47. Measure the tension in the threaded helical anchor bolts 3 after post-tensioning all bolts.

(63) 15. Install the tower 60 or other structure atop the leveling shims in the grout trough. Pour grout 37 (see FIG. 6) under the level tower or structure base flange 33 and post-tension tower anchor bolts 13, 14.

Construction Sequence and Special Features for Second Embodiment

(64) 1. At the desired location, excavate the ground for constructing the circular concrete foundation cap to a depth which allows a minimum of 1 ft. of the circular concrete foundation cap to extend above building pad subgrade. Compact the bottom of the excavation 29.

(65) 2. Spin drill the desired number of hollow bar helical anchors 187 to the desired depth. The number of hollow bar helical anchor assemblies 187 typically depends upon the number of tower anchor bolts. Hollow bar anchor pipes 184 are sectioned typically in 5 ft. to 20 ft. lengths and bolted together with threaded couplers 188. Helical discs 25 are welded around the pipe and grout ports 48 are drilled through threaded couplers 188.

(66) 3. Pressure-grout each hollow bar helical anchor 187 through grout holes or ports 48 in the hollow bar anchor pipe couplers 188. If desired, the grout can be placed sequentially from the bottom up using a packer 102 (see FIG. 14). Alternatively, grouting may be deferred until after the foundation cap is formed, i.e., after step 11 below.

(67) 4. Excavate a trench below the concrete foundation cap excavation 29 for electrical, communication, and grounding conduits 11 (see FIG. 15), if they are not routed through the concrete foundation cap 46.

(68) 5. Install and secure in place the electrical, communication, and grounding conduits (not shown) in trench 11 if under the concrete foundation cap 46. If the electrical, communication, and external grounding conduits are routed between the tower anchor bolts 13 and through the concrete foundation cap 46, place and secure the electrical, communication and external grounding conduits prior to pouring concrete for the concrete foundation cap 46. For convertible hollow bar helical anchors, place the compression plates 7 atop the coupler on the hollow bar end at or about ground level, place the helical anchor compression discs 31 atop the compression anchor plates 7, and place helical anchor bolt PVC pipes 5 or the like atop the discs 31.

(69) 6. Place and secure the internal grounding wire 12 to the hollow bar helical anchor pipes 184. Leave tails for later connection of the internal grounding wire (not shown) to the perimeter corrugated metal pipe 20, the internal corrugated metal pipes 21 and 22, and the supported structural tower base flange 33.

(70) 7. Pour the concrete/slurry leveling course 6 and the electrical, communication, and grounding trench 11 if the conduits are routed under the foundation.

(71) 8. Assemble the tower anchor bolt cage, generally designated by reference numeral 10 (see FIG. 15) which includes the template ring 15 (see FIG. 1), the embedment ring 19 along with the lap joints 45, tower anchor bolts 13, 14, the hex nut 43 above the embedment ring and the hex nut 44 below the embedment ring. Place, level, and secure the tower anchor bolt cage 10 centered in the concrete foundation cap 46 footprint.

(72) 9. Place the perimeter corrugated metal pipe 20 and the internal corrugated metal pipes 21 and 22. Drill holes 32 in the corrugated pipes for passing through the horizontally extending radial bolts 34 if the holes were not pre-drilled. Connect the internal grounding wire to the corrugated metal pipes 20, 21 and 22.

(73) 10. Insert the sleeved horizontal radial bolts 34 through the holes 32 in the corrugated metal pipes and between the sleeved tower anchor bolts 13, 14. Place nuts 35 on threaded ends beyond the bolt sleeves inside the innermost internal corrugated metal pipe 22 and outside the perimeter corrugated metal pipe 20.

(74) 11. Pour concrete and finish concrete foundation cap 46. If grouting was deferred as noted in step 3, pressure-grout each hollow bar helical anchor 187 through grout holes or ports 48 in the anchor pipe 184. If desired, the grout can be placed sequentially from the bottom up using a packer 102. Remove the template ring 15 for reuse a minimum of one (1) day after concrete cure.

(75) 12. After a minimum of three (3) days of concrete cure, or after concrete cylinder break tests determine a specified concrete strength, tension the horizontally extending radial bolts 34 from outside the perimeter corrugated metal pipe 20.

(76) 13. Place and level the helical anchor base plate 17 atop leveling shims (not shown) and a thin layer 40 of cementitious grout (see FIG. 15). After grout cure of a minimum of one (1) day, post-tension the hollow bar helical anchor assemblies 187.

(77) 14. Install the tower 60 or other structure atop the leveling shims in the grout trough. Pour grout 37 (see FIG. 6) under the level tower or structure base flange 33 and post-tension tower anchor bolts 13, 14.

Structural and Operational Advantages of Both Embodiments

(78) The helical anchor foundation of the present invention provides significant structural and operational advantages as follows:

(79) 1. The concrete foundation cap 46 is constructed at or below ground surface so the top is elevated above the surrounding ground surface and above shallow temporary flooding, and the bottom of the concrete foundation cap 46 is above ground water.

(80) 2. The bolt helical anchors 47 and the hollow bar helical anchors 187 of the helical anchor foundation 52 are tension members which pull the concrete foundation cap 46 downwardly, compressing and improving the strength of the underlying bearing soils with such a compression force that the concrete foundation cap 46 is always bearing on the underlying soils even under the greatest overturning and uplift forces transferred to the concrete foundation cap 46 from the tower structure by the tower anchor bolts 13, 14 connected to the concrete foundation cap 46.

(81) 3. The tensioning elements of the post-tensioned helical anchors, whether anchor bolts 3 or the short length of hollow bar 185, are shielded from bonding with the reinforced concrete of the concrete foundation cap 46 by sleeves, allowing the tensioning elements to elongate when pulled upward by jacks to the required post-tension. The post-tensioned anchor bolts or tendons 3 are secured in tension by nuts 28 which are threaded atop the helical anchor base plates 17 against the top of the concrete foundation cap 46, thus pulling the cap 46 downwardly with great compression against the underlying soils. Helical anchor bolts or tendons 3 may be retensioned as necessary using thread nuts 28.

(82) 4. The pull down/hold down force of the helical anchors 47, 187 results from the post-tensioning of the anchor bolts 3 or the hollow bar length 185 against the helical anchor base plates 17 atop the concrete foundation cap 46. Each helical anchor 47, 187 is pulled upwardly toward the bottom of the concrete foundation cap 46 until the resisting skin friction along the sides of the helical anchor pipe 23, 184 the compression atop the helical anchor discs 25, and the skin friction of the pressure injected grout 24 equals the post-tension on the threaded anchor bolt 3 or hollow bar length 185. The post-tension downward force atop the concrete foundation cap 46 by each helical anchor 47, 187 should exceed the determined maximum uplift of the helical anchor by a factor of 1.33 or greater.

(83) 5. The helical anchors 47, 187 can all be tension-only anchors, but preferably approximately 25 to 50% of the anchors are convertible to also act as compression anchors to limit the maximum settlement of the concrete foundation cap 46. The convertible helical anchors 27, 227 that are constructed to provide both tensions and compression capabilities are made to include compressible material 31 placed in spaces that are cast into the bottom of the leveling course 6 above the steel compression plate 7 supported by the subassembly connecting the threaded anchor bolt 3 to the helical anchor pipe 23 or the coupler 188 positioned just below the plate 7. The compressible material 31 (or space gap) allows the concrete cap foundation 46 to be pulled downwardly, compressing and consolidating the underlying soils to the required bearing strengths and allowing the convertible helical anchors 27, 227 to pull upwardly, developing the skin friction resistance equal to the helical anchor post-tension on the tensioning element.

(84) 6. Sleeved horizontally extending radial bolts 34 nutted on the ends provide steel reinforcement near the top and bottom of the concrete foundation cap 46. The sleeved radial bolts are post-tensioned to compress the concrete in the concrete foundation cap 46 horizontally. The maximum tensioning forces from bending of the concrete foundation cap 46 eliminate bolt cycling, stress reversals, and fatigue, increasing life expectancy of the foundation. The bolt sleeves of PVC pipe or the like allow the bolts to be replaced to extend fatigue life or to be replaced with greater bolt strength for additions to the supported structure or future replacement with a larger structure. The sleeved radial bolts can extend horizontally beyond the perimeter of the concrete foundation cap and be coupled to extensions of the bolts for increasing the size and load capacity of the foundation.

(85) 7. Corrugated metal pipes 20, 21 and 22 are placed in the interior and at the perimeter of the concrete foundation cap 46. The corrugated metal pipes 20, 21, and 22 provide vertical and circumferential steel reinforcement, a perimeter form, and holes therein to support and position the radial sleeved bolts 34 which provide the post-tensioned horizontal steel reinforcement.

(86) 8. The helical anchor pipes 23, 184 have holes or grouting ports 48 drilled through the anchor pipe wall to allow pressurized grout or sand cement slurry to be injected into the surrounding soil materials to improve ground conditions and strengths, increasing the skin friction with the helical anchor pipe 23, 184, welds 26 or external threads 127, and helical discs 25, and increasing the size and contact area of the anchor.

(87) 9. The bolt helical anchor pipe 23 and the hollow bar helical anchor pipes 184 have a hollow annulus 9 that provides a central vertical void in the helical anchor pipe 23, 184 for high pressure injection of grout 24 through grout holes 48 drilled through the pipe wall. The annulus 9 is filled incrementally using an inflatable packer 102 that plugs the annulus to confine the grouting to zones below the packer. After intended quantities and pressures are reached in a lower zone of the helical anchor pipe 23, 184, the packer is deflated and moved upward to grout a next higher zone.

(88) 10. The helical anchor pipes 23 preferably have a deformed outer surface from rough welds 26 that are not ground smooth around the perimeter of the pipe so as to increase friction and bond strength with pressure injected grout 24. The hollow bar helical anchor pipes 184 have an externally threaded surface that increases friction without the need for welds.

(89) 11. The constructed helical anchors 47, 187 are designed to allow easy access to determine at any time the residual tension in each helical anchor after relaxation and soil creep by ultrasonic testing. Tension determination demonstrates the helical anchor 47, 187 performance and determines when and which anchors may require maintenance retesting.

(90) 12. Installing the bolt helical anchor pipes 23 and/or hollow bar helical anchor pipes 184 is accomplished by spin drilling the anchors with helical discs 25 which auger deep down through the soil or soft rock. No soil or water is removed in connection with the helical anchor assembly 47, 187 installation and therefore environmental permits are not required for dewatering equipment, holding ponds, or disposal sites.

(91) 13. The construction of the post-tensioned helical anchors and foundation 52 requires less area and fewer construction materials than shallow foundations which require massive size and material weight to resist supported structural overturn. Therefore, the concrete foundation cap 46 in accordance with the present invention has a much smaller carbon footprint and provides environmentally conducive advantages.

(92) 14. The grout 37 poured into and confined by the grout trough 41 (see FIG. 4) to support the tower 60 is preferably mixed with rubber tire grindings and/or fiber mesh as grout additives to provide energy dampening of the tower movement.

(93) 15. Electrical, communications, and grounding conduits in trench 11 are placed and secured between the tower anchor bolts 13, 14, and extended vertically through the top of the foundation 46 and horizontally through or under the concrete foundation cap 46.

(94) 16. The electrical grounding cables are connected to the supported structure base flange 33 and external grounding cables and rods beyond the perimeter of the concrete foundation cap 46. The grounding cables are also tailed (not shown) to connect internally to the corrugated metal pipes 21 and 22, the bolt helical anchor pipes 23 and/or hollow bar helical anchor pipes 184, and the perimeter corrugated pipe 20.

(95) 17. The tower anchor bolts 13, 14 connecting the supported structure to the concrete foundation cap 46 are sleeved with PVC pipe 18 or the like and are secured with nuts 43 atop and nuts 44 below the embedment ring 19 near the bottom of the concrete foundation cap 46. The bolts are replaceable with higher strength bolts of the same size if structure loads are increased in the future as a result of structure modifications or enlargements.

(96) 18. The bolt helical anchor pipes 23 and/or hollow bar helical anchor pipes 184 are drilled deep into the ground beyond weaker shallow soils for seating in stronger and denser soil or soft rock. The deep anchoring provides a foundation support system deep into the ground below potential shallow soil failures from such events as storm surges, seismic upset forces, liquefaction, and flooding.

(97) The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to hose 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.