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what are deep foundations

Typically referred to when the foundations are deeper than 3meters below ground level.

The most common form of foundation is various forms of piled foundations.

There are other types including deep pad or deep strip foundations.


2 main types of pile include

Displacement Piles (Large and small displacement piles)

Replacement Piles


explain displacement pilling

In simple terms during the displacement pilling method, piles are driven into the ground pushing the ground out of the way, as you see in sheet piling.

Displacement pilling is good for contaminated sites where it can cost a lot to remove soil
Piles are forced into the ground by forcing or driving a solid pile or hollow casting into the ground.
Methods of installation can include drop hammer, vibration or using a jack.


explain replacment pilling

Using the replacement pilling method, soil is removed and replaced with the pile, therefore allowing for larger piles to be used.
The holes are bored either using a hollow weighted grab which is dropped and raised, removing soil as it does or using a rotary borer or auger.
A chemical such as bentonite is used to prevent the sides from collapsing or a shell made of steel is inserted into the hole
This method is quieter than the displacement method and should not result in damage to surrounding buildings.


The selection of an appropriate pile type for a given situation will need to be addressed by a number of criteria. The significate of each will differ from site to site, however the main criteria are as follows;

Location. Adjacent structures, potential for damage. Noise pollution.
Nature of the ground. Clay soils, sands, rock, demolition debris.
Cost. The most economical design that meets the foundation performance.
Structural performance. Adequately support of the loads of the building.
Durability. The ability to survive the conditions will limit the choice of material used to form the pile.