TABLE OF CONTENTS Subsurface conditions, structural requirements, site location and features, and economics generally dictate the type of foundation to be employed for a given structure.
Deep foundations, such as piles, drilled shafts, and caissons, should be considered when:
Shallow foundations are inadequate and structural loads need to be transmitted to deeper, more competent soil or rock
Loads exert uplift or lateral forces on the foundations
Structures are required to be supported over water
Functionality of the structure does not allow for differential settlements
Future adjacent excavations are expected
Pile foundations are commonly installed for bridges, buildings, towers, tanks, and offshore structures. Piles are of two major types: prefabricated and installed with a pile-driving hammer, or cast-in-place. In some cases, a pile may incorporate both prefabricated and cast-in-place elements. Driven piles may be made of wood, concrete, steel, or a combination of these materials. Cast-in-place piles are made of concrete that is placed into an auger-drilled hole in the ground. When the diameter of a drilled or augured cast-in-place pile exceeds about 24 in, it is then generally classified as a drilled shaft, bored pile, or caisson (Arts. 7.15.2, 7.2, and 7.23).
The load-carrying capacity and behavior of a single pile is governed by the lesser of the structural strength of the pile shaft and the strength and deformation properties of the supporting soils. When the latter governs, piles derive their capacity from soil resistance along their shaft and under their toe. The contribution of each of...
