Pile foundations consist of deeply placed vertical piles installed under the elevated structure. The piles support the elevated structure by remaining solidly placed in the soil. Because pile foundations are set deeply, they are inherently more tolerant to erosion and scour. Piles rely primarily on the friction forces that develop between the pile and the surrounding soils (to resist gravity and uplift forces) and the compressive strength of the soils (to resist lateral movement). The soils at the ends of the piles also contribute to resist gravity loads.
Piers are generally placed on footings to support the elevated structure. Without footings, piers function as short piles and rarely have sufficient capacity to resist uplift and gravity loads. The type of footing used in pier foundations greatly affects the foundation’s performance. When exposed to lateral loads, discrete footings can rotate so piers placed on discrete footings are only suitable when wind and flood loads are relatively low. Piers placed on continuous concrete grade beams or concrete strip footings provide much greater resistance to lateral loads because the grade beams/footings act as an integral unit and are less prone to rotation. Footings and grade beams must be reinforced to resist the moment forces that develop at the base of the piers due to the lateral loads on the foundation and the elevated home.
CMU Continuous Block
A closed foundation is typically constructed using foundation walls, a crawlspace foundation, or a stem wall foundation (usually filled with compacted soil). A closed foundation does not allow water to pass easily through the foundation elements below the elevated building. Thus, these types of foundations are said to obstruct the flow. These foundations also present a large surface area upon which waves and flood forces act; therefore, they are prohibited in V zones and not recommended for Coastal A zones. If foundation or crawlspace walls enclose space below the Base Flood Elevation (BFE), they must be equipped with openings that allow floodwaters to flow in and out of the area enclosed by the walls. The entry and exit of floodwaters will equalize the water pressure on both sides of the wall and reduce the
likelihood of the wall collapsing.