What are the main types of foundations used in construction?

Foundations are classified as shallow or deep. Shallow foundations (depth/width < 1) include: isolated footings (single columns), combined footings (multiple columns), strip footings (walls), mat/raft foundations (entire building area). Deep foundations include: driven piles (timber, concrete, steel), drilled shafts/bored piles, and caissons. Selection depends on soil conditions, load magnitude, settlement tolerance, groundwater, and economics.