Solution

Helical piles were selected for the project due to the low relative cost compared to other deep foundation options, the speed at which helical piles could be installed, and the ability to easily add extensions to achieve bearing depths. The foundation design included six, four-foot thick pile caps measuring 12 or 18 feet wide by 18 feet long. Four tension piles were located on one end of each pile cap and two compression piles were located on the other end. The tension pile configuration consisted of the Model 175 (1.75-inch) round corner square bar with a 10”-12”-14” triple-helix lead section followed by five additional 14” helix plates on extensions to support a design working load of 55 kips. The tension piles were advanced to depths to achieve installation torques between 10,000 and 11,000 ft-lb. The compression pile configuration consisted of the Model 350 (3.5-inch OD by 0.313-inch wall) hollow round shaft with an 8”-10” double-helix lead section to support a design working load of 100 kips. The compression piles were advanced to refusal on or within the limestone bedrock. With the piles taken to their respective mechanical allowable ratings, load tests were required to verify that the design capacity could be achieved. The Model 175 tension pile was load-tested to 90 kips and the Model 350 compression pile was load-tested to 150 kips. Measured deflections at design working loads were about 0.4-inch and 0.6-inch for the tension and compression piles, respectively. Creep movement of the piles at the maximum test loads were within the specified limits. The production piles were installed to depths ranging from 21 to 63 feet. The 36 piles were installed in two days.