Full/Direct Drilled Displacement piles (FDP)

FDP piles are installed with a similar technique as the CFA piles except no or a relatively small amount of soil cuttings (spoils) are removed from the ground. The auger at the tip loosens the soil followed by a “bulb” the same diameter of the borehole.  The bulb pushes the soil to the sides, densifying the surrounding soil, thereby increasing the pile load bearing capacity.   Concrete is then pumped through the hollow drill rods and forced into the borehole as the bulb is slowly retrieved.  Once the auger is removed from the ground and the borehole is filled with concrete, steel reinforcing is placed.  The steel reinforcing can consist of a circular cage,  one center bar, or both.  These economical piles generally range from 14- to 18-in diameter with lengths up to approximately 200-ft. They have been used extensively where soil cuttings are restricted due to environment requirements.