Major criteria in foundation design

A foundation must carry the structure's load safely and economically. The major criteria are:

1. Location and depth: the foundation must be placed below the zone of seasonal moisture change, frost, scour, swelling/shrinkage and made ground, and safe from adjacent excavations.
2. Safety against shear failure (bearing capacity): the contact pressure must not exceed the net safe bearing capacity of the soil, i.e. a factor of safety of about 2.5-3 against shear failure.
3. Tolerable settlement: total settlement and especially differential settlement must stay within permissible limits so the superstructure is not damaged.
4. Structural adequacy: the footing/raft/pile itself must be strong enough in bending, shear and punching.
5. Durability and economy: it must resist chemical attack and groundwater, be buildable with local skill and materials, and be the cheapest solution that meets criteria 1-4.