Foundations transfer loads from the building or individual columns to the earth. Types of foundations are 1. isolated bases for individual columns 2. combined bases for several columns 3. rafts for whole buildings which may incorporate basements All the above types of foundations may bear directly on the ground or be supported on piles. Only isolated and combined bases are considered. The type of foundation to be used depends on a number of factors such as 1. the soil properties and conditions 2. the type of structure and loading 3. the permissible amount of differential settlement
The choice is usually made from experience but comparative designs are often necessary to determine the most economical type to be used.