Engineering Term of the Month
DEEP FOUNDATION
Deep foundations are used to transmit loads through upper weaker or compressible layers to a competent stratum below , to provide support where shallow foundations are not practical such as below water or in close proximity to existing structures , and to provide uplift resistance or lateral capacity . Deep foundations include driven or drilled piles and piers / caissons . Piers or caissons are simply large diameter piles , but the design process is somewhat different . US Army Corps of Engineers defines the distinction between a pile and a pier as a caisson having a diameter of 30 inches or greater .
There are many differing types of deep foundations . These include timber and steel H-piles , precast concrete piles , cast-in-place concrete piles , pressure-injected- footings , steel pipe piles , straight-shaft or belled piers , and others . Selection of the deep foundation type should consider the needed capacity , subsurface conditions , length , location and topography , regional availability , project-specific restrictions , and economy .
Deep foundation design should include a coordinated effort between geotechnical and structural engineers and geologists in preparation of the overall foundation design , including plans and specifications .
Sources :
• NAVFAC Foundations and Earth Structures Design Manual 7.2
• US Army Corps of Engineers , Design of Pile Foundations , EM 110-2-2906
• Departments of the Army and the Air Force , Technical Manual No . 5-818-1 , Soils and Geology Procedures for Foundation Design of Buildings and Other Structures
• United States Department of Defense , Unified Facilities Criteria ( UFC ), UFC 3-220-01A , Deep Foundations
• FHWA Design and Construction of Driven Pile Foundations – Volume 1