Retrofit reinforcing structure addition and method for wind turbine concrete gravity spread foundations and the like

1. A retrofit reinforcing structure addition for an existing spread foundation that has a central pedestal and a horizontal spread section, the retrofit reinforcing structure addition comprising:

a collar surrounding the central pedestal of the existing spread foundation, a base of the collar pressing on an upper surface of the horizontal spread section of the existing spread foundation;

a plurality of radial bolts each having an outermost, tensioning-nut carrying end and an innermost, nut-free end, the radial bolts extending in a generally horizontal orientation from an outer perimeter of the collar, and through the collar, such that the innermost nut-free ends extend into a plurality of adhesive-filled holes in the central pedestal, respectively, whereby the adhesive-filled holes secure the innermost nut-free ends of the radial bolts into the central pedestal; and

a plurality of soil and/or rock anchor bolts extending in a generally vertical orientation through the collar and the horizontal spread section and into an underlying soil and/or rock substrate below the horizontal spread section.

2. The retrofit reinforcing structure addition as set forth in claim 1 , wherein said soil and/or rock anchor bolts and said radial bolts are post tensioned.

3. The retrofit reinforcing structure addition as set forth in claim 1 , wherein said existing spread foundation has a tower already supported thereon when the retrofit reinforcing structure addition is added.

4. The retrofit reinforcing structure addition as set forth in claim 1 , wherein said collar includes a shape sustaining outer member having a perimeter greater than an outer diameter of the pedestal to define a region between the shape sustaining outer member and the central pedestal, said region having cementitious material poured therein which hardens to form a body of cementitious material surrounding the pedestal and contained within the shape sustaining outer member.

5. The retrofit reinforcing structure addition as set forth in claim 4 , wherein the perimeter of said shape sustaining outer member is generally circular.

6. The retrofit reinforcing structure addition as set forth in claim 5 , wherein said shape sustaining outer member is a corrugated metal pipe (CMP), against which CMP the tensioning nuts carried by the radial bolts are tensioned.

7. The retrofit reinforcing structure addition as set forth in claim 4 , wherein said radial bolts include a plurality of layers of extending radial bolts vertically spaced from one another.

8. A retrofitted reinforced gravity spread foundation supporting a tower or a wind turbine comprising:

a concrete gravity spread foundation having a central pedestal and a horizontal spread section, the tower or the wind turbine being mounted on the central pedestal;

a reinforcing structure addition added to the concrete gravity spread foundation and including a supporting member surrounding the central pedestal of the concrete gravity spread foundation, a base of the supporting member pressing on an upper surface of the horizontal spread section of the concrete gravity spread foundation;

a plurality of post-tensioned radial bolts extending in substantially horizontal orientation through the supporting member and into a plurality of adhesive-filled holes, respectively, formed in the central pedestal securing the radial bolts therein; and

a plurality of post-tensioned anchor bolts extending in a substantially vertical orientation through the supporting member and the horizontal spread section and into an underlying soil and/or rock substrate.

9. The retrofitted reinforced gravity spread foundation as set forth in claim 8 , wherein said post-tensioned radial bolts are arranged to be in an upper layer, a middle layer and a lower layer, said layers being spaced vertically from one another.

10. The retrofitted reinforced gravity spread foundation as set forth in claim 9 , wherein the post-tensioned radial bolts in each layer are offset with respect to the post-tensioned radial bolts in other layers such that, if the three layers were placed directly on top of one another, the post-tensioned radial bolts in one layer would not be in vertical alignment with the post-tensioned radial bolts in the adjacent layers.

11. The retrofitted reinforced gravity spread foundation as set forth in claim 8 , wherein said supporting member is a collar.

12. The retrofitted reinforced gravity spread foundation as set forth in claim 11 , wherein said collar includes a shape sustaining member having a perimeter greater than an outer diameter of the central pedestal to define a region between the shape sustaining member and the central pedestal, a cementitious material being poured into said region and hardened to form a body of cementitious material surrounding the central pedestal and contained within the shape sustaining member.

13. The retrofitted reinforced gravity spread foundation as set forth in claim 12 , wherein the perimeter of said shape sustaining member is generally circular.

14. The retrofitted reinforced gravity spread foundation as set forth in claim 13 , wherein said shape sustaining member includes a corrugated metal pipe (CMP).

15. The retrofitted reinforced gravity spread foundation as set forth in claim 14 , wherein said post-tensioned radial bolts extend through said CMP and said body of cementitious material.

16. The retrofitted reinforced gravity spread foundation as set forth in claim 8 , wherein a lower portion of said central pedestal engages a central upper portion of said horizontal spread section at an engagement interface, said plurality of post tensioned anchor bolts reinforcing the engagement interface between the lower portion of the central pedestal and the central upper portion of the horizontal spread section.