Piles are generally used to spread the load of a building through soft and/or unstable ground, to firmer ground further down. Piles are usually made of concrete, either precast or poured in-situ on site. In domestic housing situations the concrete or steel piles are joined at the top with a reinforced concrete beam, commonly called a ring beam, which connects piles on the perimeter of the property and onto which the superstructure, I.E. Brickwork and/or Blockwork is built.
Essentially there are two types of pile. Replacement piles are piles which are put into holes dug or augered out of the earth. The concrete, or steel, simply replaces the earth, clay etc which has been excavated. Displacement piles are precast or pre-formed piles which are driven into the ground by a huge piling hammer. These displace the earth they are driven through.
When choosing a piling system for foundation use there are 4 main things to base a decision on.
- 1: The load (weight) of the building or structure to be supported.
- 2: The Cost of piling versus other foundation types.
- 3. The physical possibilities of getting very heavy piling equipment to the site without causing more disruption (noise etc) than necessary
- 4. The condition of the ground and strata.
Piling is being used more often these days than in past years. This is largely because of the huge increases in cost of carting away the many tonnes of soil required for a normal strip or raft foundation. The closer together piles are placed, the less the diameter of them needs to be and in some cases, especially in situations where a lot of subsidence has occurred, piles can be drilled through existing floor slabs to stop them sinking any further. This type of piling is called mini piling. Micro piles, usually even smaller diameters, are used where access is very much restricted. Piles can also be used when underpinning a property.