The foundation is he lower portion of the building, usually located below the ground level, which transmit the load of super structure to sub soil

Functions of foundation

·         Reduction of load intensity

·         Even distribution of load

·         Provision of level surface

·         Lateral stability

·         Safety against undermining

·         Protection against soil movements

Types of foundation

·         Shallow foundation

·         Deep foundation

Shallow foundation

If the depth of foundation is less than or equal to width of foundation it is called as shallow foundation

Types of shallow foundation

·         Spread footing

·         Combined footing

·         Strap footing

·         Mat foundation

Spread footing

Spread footing is those which spread the super imposed load to of a wall or column over the large area

Spread footing support either a column or a wall

It has the following types

·         Single footing

·         Stepped footing

·         Sloped footing

·         Wall footing without step

·         Stepped footing for wall

·         Grillage foundation

Combined footing

A spread footing which supports two are more columnsis termed as combined footing It has the following types

·         Rectangular combined footing

·         Trapezoidal combined footing

·         Combined column wall footing

Trapezoidal footing

If the independent footings of two columns are connected by a beam it is called as strap footing

A strap footing may be used where the distance between the columns is so great that a combined trapezoidal footing becomes quite narrow

The strap beam does not remains in contact with soil and thus does not transfer any pressure to the soil

Mat foundation

A raft or mat is a combined footing that covers the entire beneath a structure and supports all walls and columns. It is used when the allowable soil pressure is low are the building loads are heavy. It is used to reduce the settlement above highly compressible soil

Rafts may divided into three types

·         Solid slab system

·         Beam slab system

·         Cellular system

Deep foundation

If the depth of foundation is equal to or more than the width of the foundation is called deep foundation

Types

·         Deep strip rectangular or square footing

·         Pile foundation

·         Pier foundation or drilled caisson foundation

·         Well foundation or caissons

Deep strip footing

Whenever the depth of strip footing is more than the width it is called as deep strip footing

Pile foundation

it is a type of deep foundation in which the loads are taken to a low level by means of vertical members which may be timber or concrete or steel

Types of pile foundation

·         End bearing pile

·         Friction pile

·         Combined end bearing and friction pile

·         Compaction pile

End bearing piles

End bearing piles are used to transfer load through water or soft soil to a suitable bearing stratum

Such piles are used to carry heavy loads to hard strata

Multi storied buildings are invariably founded on end bearing piles, so that the settlements are minimized

Friction piles

Friction piles are used to transfer loads to a depth of a friction load carrying material by means of skin friction along the length of the pile

These piles mostly used in granular soil

Combined end bearing and friction pile

These are the piles which transfer the super imposed load both through side friction as well as end bearing

Such piles are more common, especially the end bearing piles are passed through granular soil

Compaction piles

These piles are used o compact loose soil thus increasing there bearing capacity The pile tube driven to compact the soil is gradually taken out and sand is filled in its place thus forming the sand pile

Pier foundation

A pier foundation consist of a cylindrical column of large diameter to support transfer large super imposed loads to the firm strata below

Generally pier foundation is shallower in depth than the pile foundation

It has two types

·         Masonry

·         concrete pier

Drilled caissons

Well foundation or caissons are box like structures –circular or rectangular which are sunk from the surface of either land or water to the desired depth

Caisson foundations are used for major foundation work such as

Bridge pier and abutments in river

Wharves and quay walls docks

Large water front structures such as pump houses, subjected to heavy vertical and horizontal loads

Well foundations are caissons are hollow from inside, which may filled withstand and are plugged at the bottom, the load is transferred to the perimeter wall called as steining.