Answer by Rakshita Nagayach:
The points to be considered are:
- Safe Bearing Capacity of the soil: If the soil has a high safe bearing capacity, foundation of smaller depth and surface area would do and vice-versa.
- Dead and live load on the superstructure: A residential building will have comparatively less live and dead load than a library of the same size. Hence the overall size of a foundation depends on the loads.
- Expected air and earthquake loads: If the building is a high rise one, or if it is situated in earthquake prone area, there are high chances of uprooting of foundations. Thus size, specially depth of a foundation depends on these factors too.