Expanded-base piles are also known as Franki piles, pressure injected footings (PIF’s), or belled caissons. They are constructed like traditional bored piles or caissons except that the base of the shaft is expanded and compacted by placing zero slump concrete at the bottom and ramming it with a large hammer. This process forms a bulb-like shape at the base before placing the concrete backfill in the remainder of the shaft. If required by design, a steel reinforcement cage can be installed into the wet concrete for additional load bearing capacity.
- Expanded-base piles have a higher load bearing capacity in poor or non-cohesive soils compared to similar techniques due to the additional tensile and end-bearing capacity developed by addition of the expanded base.