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Last edited 14 Jul 2021
- The nature of the load requiring support.
- Ground conditions.
- The presence of water.
- Space availability.
- Sensitivity to noise and vibration.
- Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.
- Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity.
 Types of shallow foundations
|Trench fill foundation.||Rubble trench foundation.||Raft foundation.|
 Strip foundations (or footings)
Rubble trench foundations are a further variation of trench fill foundations, and are a traditional construction method which uses loose stone or rubble to minimise the use of concrete and improve drainage. For more information, see Rubble trench foundations.
Raft foundations are slabs that cover a wide area, often the entire footprint of a building, and are suitable where ground conditions are poor, settlement is likely, or where it may be impractical to create individual strip or pad foundations for a large number of individual loads. Raft foundations may incorporate beams or thickened areas to provide additional support for specific loads. For more information, see Raft foundations.
 Types of deep foundations
|Pile driver||Sheet piles||Diaphragm wall|
Generally piles are classified as; end-bearing piles (where most of the friction is developed at the toe of the pile, bearing on a hard layer), or friction piles (where most of the pile-bearing capacity is developed by shear stresses along the sides of the pile, suitable when harder layers are too deep).
Piles are most commonly; driven piles prefabricated off site and then driven into the ground, or bored piles that are poured in situ. If the boring and pouring takes place simultaneously, the piles are called continuous flight augured (CFA) piles.
 Mini piles (or micro piles/micropiles)
By placing piles directly adjacent to one another, a permanent or temporary retaining wall can be created. These can be closely-spaced contiguous pile walls, or interlocking secant walls, which depending on the composition of the secondary intermediate piles can be hard/soft, hard/firm or hard/hard secant walls.
Diaphragm walls are made by excavating a deep trench that is prevented from collapsing by being filled with engineering slurry such as bentonite and then the trench is filled with reinforced concrete panels, the joints between which can be water-tight.
Caissons are watertight retaining structures sunk into the ground by removing material from the bottom, typically this might be suitable for building structures below water level. For more information, see Caisson.
If a very large amount of material is excavated (for example, where there is a deep basement), it may be sufficient that the relief of stress due to the excavation is equal to the applied stress from the new construction. As a result, there should be little effective change in stress and little settlement.
 Related articles on Designing Buildings Wiki
- Bearing capacity.
- Compensated foundation.
- Continuous flight auger piles.
- Driven piles.
- Geothermal pile foundations.
- Ground anchor.
- How deep should foundations be?
- How to design a pad foundation.
- Pad foundation.
- Pile foundations.
- Principles of foundations.
- Raft foundation.
- Retaining walls.
- Rubble trench foundation.
- Screw pile foundations.
- Stepped foundation.
- Strip foundation.
- Trench fill foundation.
- Underwater foundations.
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