how many types of foundation

 1. Shallow Foundation

Shallow foundation is a type of foundation that transfers loads to the very near the surface. Shallow foundations typically have a depth to width ratio of less than 1 (D < B). Shallow foundation itself can be various types.

Classification of Shallow Foundation:

On the basis of design, the shallow foundation are classified as:

• Wall Footing
• Isolated column or Column Footing
• Combined Footing
• Cantilever/Strap Footing
• Mat/Raft Foundation

Wall Footing

This type of foundation runs continuous along the direction of the wall and helps to transmit the load of the wall into the ground. Wall footing are suitable where loads to be transmitted are small and are economical in dense sands and gravels. In this type of foundation the width is 2-3 times the width of the wall at ground level. Wall footing may be constructed through stone, brick, plain or reinforced cement concrete.

Isolated column/Column Footing

Column footing are suitable and economical for the depth greater than 1.5m. In this type of foundation the base of the column is enlarged. Column footing is in the form of flat slab and may be constructed through plain or reinforced concrete.

Combined Footing

Combined footings are those foundations that are made common for two or more columns in a row. It is used when the footing for a column may extend beyond the property line. It is also suitable when the two columns are closely spaced and the soil on which the structure resist is of low bearing capacity. It may be rectangular or trapezoidal in shape.

Cantilever/Strap Footing

When an edge footing cannot be extended beyond the property line the edge footing is linked up with the other interior footing by means of a strap beam. Such footings are called as strap footing. It is also know as cantilever footing.

Mat/Raft Foundation

A mat foundation is a combined footing which covers the entire area beneath of a structure and supports all the walls and columns. It is also known as raft foundation. Mat foundation is applicable when:

• Allowable bearing pressure is low.
• The structure is heavy.
• The site is with highly compressible layer.

2. Deep Foundations

Deep foundations are those founding too deeply below the finished ground surface for their base bearing capacity to be affected by surface conditions, this is usually at depths of 3 meter below finished ground level. Deep foundations can be used to transfer the load to a deeper, more competent strata at depth if unsuitable soils are present near the surface.

Classification of Deep Foundation

The deep foundation can be further classified into following types:

• Pile Foundation
• Pier Foundation
• Well (Caissons) Foundation

Pile Foundation

Pile is a slender member with small area of cross-section relative to its length. They can transfer load either by friction or by bearing. Pile foundation are used when:

• The load is to be transferred to stronger or less compressible stratum, preferably rock.
• The granular soils need to be compacted.
• The horizontal and the inclined forces need to be carried from the bridge abutments and the retaining walls.

Pier Foundation

Pier foundation are underground cylindrical structural member that support heavier load of the structure which shallow foundations cannot resist. Unlike pile foundation, pier foundation can only transfer load by bearing. Pier foundation are shallower in depth than the pile foundation. Pier foundation are used when:

• The top strata is a decomposed rock underlying as sound rock strata.
• The soil is a stiff clay that occurs large resistance for driving the bearing pile.

Well foundation

It is a type of deep foundation which is generally provided below the water level for bridges. Cassions or well have been in use for foundations of bridges and other structures since Roman and Mughal periods. The term 'cassion' is derived from the French word caisse which means box or chest.