friction pile

When the soil is so soft that even friction piles will not support the building load, the final option is the use of a floating foundation, making the building like a boat that obeys Archimedes' principle-it is buoyed up by the weight of the earth displaced in creating the foundation.

Since even the archaic mud is too weak in this concentrated load application for conventional vertical friction piles, large diameter tubular piles were driven (inside cofferdams) at angles, forming a "battered" (splayed) footing, through the archaic muds into the firm aggregated sand, mud, and gravel of the Alameda formation.