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.
- The nature of the load requiring support.
- Ground conditions.
- The presence of water.
- Sensitivity to noise and vibration.
- Proximity to other structures and loading
- 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.
See also: How to design pad foundations.
See also: Types of pad foundation.
 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
The stunt aimed at highlighting ongoing delays to its repair, as the 133-year-old west London bridge has been closed to traffic since April 2019 when cracks appeared in its pedestals.
Uninhabited Aerial Vehicles (UAVs) have been used to undertake a survey of the Lloyd’s building’s external façade in the heart of the City of London.
The petition calls on the government to remove VAT on refurbishment projects and raise VAT on non-Passivhaus new-build construction to 20 per cent. Retrofitting is carbon-efficient but the current VAT regime privileges new build over refurbishment.
Directors of the IHBC and the Victorian Society are among those whose opinions are featured in the RICS in-house publication Modus as it explores heritage impacts in England’s planning proposals.
Glasgow City Heritage Trust (GCHT) 3-day online conference aimed at anyone working, or interested in working, within the building and heritage sectors.
One way in which these old rigs can be remarkably useful is that the subsurface rig can provide the ideal skeleton for coral reefs, allowing the remarkable ecosystems beneath the waves come into their own.
A new company – Birnbeck Holdings Limited – has now been set up by CNM Estates which has purchased Birnbeck Island and the historic pier.
The publication offers research to help answer the question: ‘How can the heritage sector adapt and thrive in the digital age’?
A stunning Victorian Bath House has been uncovered during works on creating the city’s first public park in over 100 years.
The Inquiry is into ‘21st Century Places – Values & Benefits.