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

A retrofitted reinforced gravity spread foundation for a tower or wind turbine comprising:

• a concrete gravity spread foundation having a central pedestal and a horizontal spread section, a tower or a wind turbine being mounted on the central pedestal;
• a retrofit reinforcing structure addition including a collar encircling the central pedestal of the spread foundation, a base of the collar pressing on an upper surface of the horizontal spread section of the foundation;
• a plurality of post-tensioned radial bolts extending horizontally from an outer perimeter of the collar, through the collar and into the pedestal;
• and
• a plurality of post-tensioned soil, and/or rock anchor bolts extending vertically from an upper surface of the collar, through the horizontal spread section and into an underlying soil and/or rock substrate.

A method of installing a retrofit spread foundation reinforcing structure addition onto an existing concrete gravity spread foundation having a central pedestal and a spread section and supporting a tower or wind turbine, the retrofit spread foundation reinforcing structure addition including an annular cementitious collar having a shape sustaining member at its outer perimeter, a plurality of radially extending bolts extending horizontally through the collar and into the central pedestal, and a plurality of vertically oriented soil and/or rock anchor bolts extending downwardly through the collar and the spread section of the foundation, the method comprising the steps of:

• constructing temporary turbine supports;
• excavating soil from atop the spread section of the foundation for construction of the retrofit collar;
• drilling a plurality of horizontally extending core holes in the sides of the pedestal for the radial bolts;
• inserting radial bolts into said horizontally extending core holes in the sides of the pedestal;
• securing the inner ends of the radial bolts with epoxy or similar adhesive;
• inserting multi-plate corrugated metal pipe (CMP) sections over the radial bolts and bolting the CMP sections together to form said shape sustaining member which defines a generally annular ring around the central pedestal of the foundation;
• placing PVC tubes in a vertical orientation in the generally annular ring for the soil and/or rock anchor bolts to be drilled through and securing the tubes for concrete pour;
• pouring concrete into the generally annular ring between the CMP sections and the outer surface of the central pedestal;
• drilling and installing soil and/or rock anchor bolts, centralized in said PVC tubes and grouted in place;
• post-tensioning the radial bolts;
• and
• post-tensioning the soil and/or rock anchor bolts.