TYPES OF FOUNDATION

Types of foundation.

1.      Concrete strip FOUNDATION.

ü  They are frequently used.

ü  They consist of continuous mass concrete strips poured in the bottom of the trenches.

ü  These foundations supports load bearing walls which are centered on the concrete strips to spread the pressure from the walls, roofs, and other floor loads evenly.

ü  The concrete strip is usually a uniform width and depth.

ü  The foundation must be wide and deep enough to avoid soil movement that could cause instability

ü  Depending on soil conditions, the max depth may be 900mm.

ü  The concrete must be at least as thick as its projection from the base of the wall.

ü  This ensures that the pressure of the building loads are distributed in the concrete at an angle of 45°.

2.    Deep strip FD

The deep strip foundation is a variation of strip foundations.

Deep strip foundations are usually dug out with a mechanical excavator, which cuts narrow trench that is backfilled with the concrete up to the ground level.

These foundations use more concrete ,but reduce the cost of masonry walls and may remove the use of timber support for the trenches.

3.    Raft foundation

The best solution if the soil has a poor bearing capacity or if the building loads are quite small, because  the cost of digging separate foundations is eliminated. The oversite concrete slab that's forms the ground floor becomes the raft foundations.

The slab can be thickened at the edges with an edge beam and thickened underneath internal load bearing walls.

 Mesh reinforcement increases the strength of the raft foundation and distributes the pressures of the building loads evenly.

4.    Piled foundation.

A pile is basically a long cylinder of a strong material such as concrete that is pushed into the ground so that structures can be supported on top of it.

Pile foundations are used in the following situations:
When there is a layer of weak soil at the surface. This layer cannot support the weight of the building, so the loads of the building have to bypass this layer and be transferred to the layer of stronger soil or rock that is below the weak layer.

When a building has very heavy, concentrated loads, such as in a high rise structure.

Pile foundations are capable of taking higher loads than spread footings.

There are two types of pile foundations, each of which works in its own way.

End Bearing Piles

In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock. The load of the building is transferred through the pile onto the strong layer. In a sense, this pile acts like a column. The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer.

Friction Piles

Friction piles work on a different principle. The pile transfers the load of the building to the soil across the full height of the pile, by friction. In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil.

To visualize

 how this works, imagine you are pushing a solid metal rod of say 4mm diameter into a tub of frozen ice cream. Once you have pushed it in, it is strong enough to support some load. The greater the embedment depth in the ice cream, the more load it can support. This is very similar to how a friction pile works. In a friction pile, the amount of load a pile can support is directly proportionate to its length.

5.    Pad foundation.

They are isolated foundations that support the concrete columns or free-standing brick piers.

A square concrete pad foundation distributes the load evenly over the ground.

The size of the pad foundation depends on the total building loads and the loads bearing capacity of the soil.