Solving Variable Bedrock Challenges with Ductile Iron Piles-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the use of ductile iron piles (DIPs) for the foundations of a 375-foot pedestrian bridge at Moffitt Cancer Center in Tampa, Florida. The bridge crossed a major road and connected to a new bed tower. Its foundations faced heavy loads, limited site access, and highly variable limestone beneath loose-to-medium-dense sands and thick plastic clay.<br /><br />The project required 13 foundations and ultimately used 184 DIPs. Each pile was a prefabricated, top-driven ductile cast-iron pipe assembled in segments. The design selected 118/7.5 piles, with external grout used on all piles. For friction capacity, piles were driven while grout was pumped to create a bond zone around the pile; reinforcement could provide additional tension capacity. The system was considered alongside cast-in-place piles, drilled piers, and driven steel piles.<br /><br />Key design challenges included variable pile lengths, shallow or deep refusal, uncertain grout returns in porous limestone, possible pile necking in clay, and splice locations in high-moment areas. The team addressed these issues with installation criteria informed by local experience, laboratory bending tests of spliced piles, and a site-specific load-test program. Load tests evaluated compression, tension, and lateral performance.<br /><br />Construction averaged about 20 piles per day and finished in 75% of the scheduled duration. Piles ranged from 32 to 70 feet, averaging 47 feet. Vibration monitoring remained well below the specified threshold, and the equipment was also used in low-overhead areas. Early pile “walking” was reduced by drilling deeper pilot holes. The project demonstrated how DIPs can provide an adaptable foundation solution where bedrock depth and quality vary.

Keywords

ductile iron piles

pedestrian bridge

foundation design

Moffitt Cancer Center

Tampa Florida

limestone variability

pile load testing

grouted piles

deep foundations

construction vibration