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Commercial Foundations Case Studies: Helical Anchors for Tyndall Air Force Base Array Field – Panama City, FL

Problem:

A 200-foot-long by 60-foot-wide photovoltaic array field was being constructed at Tyndall Air Force Base near Panama City, Florida. The project site is adjacent to an existing structure, so the need for a deep embedment system that produces minimal vibrations was essential.

The photovoltaic arrays were mounted on steel base structures which were attached to 6-5/8 inch round shaft helical anchors. These large diameter shafts were selected to support the arrays in order to resist uplift loads due to high winds and to resist lateral movement due to loose soils present at the site. A 36-inch-square collar, at 18 inches thick, was also constructed around each anchor at the surface to help resist these lateral loads.

Location: Panama City, FL
Alpha Solution:

A total of forty-four (44) AB Chance 6-5/8 inch round shaft pipe anchors were installed with an 8”-10” double-helix lead section to embedment depths of 15 feet. The anchors were designed to resist working loads of 3 kips in compression, 3 kips in tension and 1.5 kips of horizontal load (FOS > 2).

The anchors were installed with a John Deere Model 200D Excavator with a 45 kip pro-dig drive head that also included a pro-dig wireless torque monitoring system. The system was equipped with a handheld GPS data recorder to relay torque readings to the pier installers. These readings were saved and printed for the project engineer. The installation of all 44 anchors took three days to complete.