Franki piles, also known as a driven cast in-situ pile (DCIS), are high-capacity, cast-in-place elements constructed using a drop weight and casing.
A 400mm to 600mm diameter steel casing is vertically positioned at a planned location.
Gravel/sand or very dry concrete mix is introduced into the bottom of the casing and a steel hammer with a diameter slightly smaller than the casing then repeatedly dropped inside. The mix locks into the bottom of the casing and the repeated blows of the drop weight advance the casing to the design depth.
The casing is stopped from advancing further and additional drops of the hammer eject the dry mix out of the bottom of the casing.
Additional dry mix is added and driven from the casing until an enlarged base is formed. Reinforcing steel and concrete are then placed in the casing and the casing is removed.