The load of the structure is ultimately transmitted to the soil is by its foundations. But soil is weaker than materials of the structure steel or concrete, a greater area or volume of soil is involved in order to carry the load. Type of foundation and type of soil are closely related. If more weight is to be transmitted more area required or type of structure should be altered.

Stability of structure is depended on the soil foundation system, so worst condition must be considered.

Types of foundations

The broad classification is shallow and deep, according to depth. Shallow foundation is that the depth is less than its width and deep when exceeds the width. Shallow types are footings and raft or mats. Deep types are piles, piers, wells.

If a basement floor is given mat over piles foundation is the best method. Floating foundation is that the load of soil excavated is replaced by the weight of the structure.

The principle of foundation is the load is spread over the soil, or geometrical stability is provided to the structure. To select a foundation type the load of the structure is to be studied, the soil condition underneath is also examined. The soil for a depth 1.5 times the least width of the structure is examined for bearing. Bearing capacity of soil is that the load taken per square meter of area. When load is large the area of footing is given more not the depth.

Foundation selection and soil condition

  • Compact sand-spread footing
  • Firm clay-spread footing
  • Loose sand – raft foundation is suitable
  • Soft clay to great depth – piles friction type
  • Soft clay over rock- end bearing piles

The soil may be hard for some depth but after which it is weak piles is a suitable type foundation. The bore is taken and is studied.