A deep foundation is a type of foundation

Foundation (architecture)

A foundation is the lowest and supporting layer of a structure. Foundations are generally divided into two categories: shallow foundations and deep foundations.-Shallow foundations:...

 distinguished from shallow foundations by the depth they are embedded into the ground. There are many reasons a geotechnical engineer would recommend a deep foundation over a shallow foundation, but some of the common reasons are very large design loads, a poor soil

Soil

Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 at shallow depth, or site constraints (like property line

Property line

Property line describes the legal boundary of a parcel of land. The boundary is established by a professional surveyor using a transit and or modern Global Positioning System technology...

s). There are different terms used to describe different types of deep foundations including the pile (which is analogous to a pole

Pole

-General:*Poles, people originating from inbitating or inhabiting the country of Poland*Pole -Fictional:*Jill Pole, a fictional character from C. S...

), the pier (which is analogous to a column

Column

A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

), drilled shafts, and caisson

Caisson (engineering)

In geotechnical engineering, a caisson is a retaining, watertight structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships. These are constructed such that the water can be pumped out, keeping the working...

s.