- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 12 Jun 2018
See also: How to design pad foundations.
See also: Types of pad foundation.
Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics. They can be used to help to prevent settlement and other movements of structures and can permit construction on ground that might otherwise have insufficient bearing capacity.
There are a very wide range of foundation types suitable for different applications, depending on considerations, such as:
- The nature of the load requiring support.
- Ground conditions.
- The presence of water.
- Sensitivity to noise and vibration.
- Proximity to other structures.
- Project time-frames.
Very broadly, foundations can be categorised as shallow foundations or deep foundations. 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 (more than 3 m from the surface) may be necessary where the bearing capacity of the surface soils is insufficient to support loads imposed.
Pad foundations are generally shallow foundations, but can be deep depending on the ground conditions. They are a form of spread foundation formed by rectangular, square, or sometimes circular concrete ‘pads’ that support localised single-point loads such as structural columns, groups of columns or framed structures. This load is then spread by the pad to the bearing layer of soil or rock below. Pad foundations can also be used to support ground beams.
They are generally of a uniform thickness, but sometimes the upper face may be sloped or stepped. Their plan shape will depend on the nature of the applied load and the allowable bearing capacity of the layers below. Their thickness must be sufficient to distribute the load across the plan shape. They are generally reinforced on all but the smallest structures, with the reinforcement allowing higher loads to be imposed and the construction of shallower pads which require less excavation and use less concrete.
The arrangement of pad foundations will vary depending on the nature of the structure they are supporting, the loads imposed, the allowable bearing capacity of the layers below and the space available on site. They may be:
- A series of discrete, well-separated pads.
- Balanced base pads that support more than one point load.
- Continuous pads, where there are a number of point loads close together.
- Pad and beam, where a series of pads support a continuous beam.
Pad foundations can be selected as they do not require much excavation, and are generally suitable where the bearing capacity of ground is sufficient at relatively low depths. However, they can be large in plan shape and may not be effective against differential settlement, uplift forces or wind forces.
 Related articles on Designing Buildings Wiki
- Compensated foundation.
- Continuous flight auger piles.
- Driven piles.
- Geothermal pile foundations.
- Ground anchor.
- How deep should foundations be?
- How to design a pad foundation.
- Pile foundations.
- Raft foundation.
- Screw piles.
- Strip foundation.
- Temporary works.
- Trench fill foundation.
- Types of pad foundation.
- Types of raft foundation
Featured articles and news
Dr Nicholas Falk, director of the URBED Trust, explains why metro cities are the future of urbanisation.
From next week, UK firms can bid for a share of a £12.5m fund to boost productivity, performance and quality.
A right to light generally refers to the right to receive sufficient light through an opening.
Interference and compatibility - the effects of electromagnetic fields in the workplace.
Important action is being taken to inspire young people to train as engineers.
A survey of Leicester’s historic buildings resulted in local listing being taken more seriously.
Demolition is the most high risk activity in the construction sector. Read our introductory article here.
BSRIA report on the domestic boiler market, with China recording the most 'dynamic market uptake'.
Do we really know everything important about the impacts of our infrastructure projects? And if we don’t, does it matter?
Former Chief executive Richard Howson blames government for being 'poor payers'.