- Project plans
- Project activities
- Legislation and standards
- Industry context
- Specialist wikis
Last edited 11 Oct 2020
Very broadly, foundations can be categorised as shallow or deep:
- 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 sufficient to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity.
Compensated foundations are a type of deep foundation, which work on the principle that if the weight of material excavated equals the weight of the building added, the soil is subjected to no additional stresses. They are also known as ‘floating foundations’ as the structure acts in a similar way to a ship’s hull.
The relief of stress due to the excavation is approximately balanced by the applied stress of the foundation, resulting in a negligible net stress. As a result there may be little consolidation settlement experienced.
- A simple construction process with minimal impact on adjacent structures.
- They can be integrated with other foundations in more complex situations, such as piling.
- They can contribute to protection from rising damp, thermal insulation, drainage, and so on.
Where soil is compressible, a raft foundation may be formed as a compensated foundation. In this case, the raft slab is provided to a depth that the weight of the excavated soil is equal to the raft slab weight plus that of the structure to be supported. This can be appropriate when constructing buildings on soft clay or loose sand, as settlement can be significantly reduced.
Compensated piled raft foundations are typically used where the soil provides only modest bearing capacity, meaning that piles are necessary to carry some of the load. This can be necessary, for example, in the case of soft clay, which may undergo settlement due to reclamation filling or dewatering processes, during which the soil may settle away from the raft base.
 Related articles on Designing Buildings Wiki
Featured articles and news
Fropm practice to research and the business of materials.
Terms, histories, theories and practices.
Alteration and everything else before demolition.
And CIOB's response.
Presidential update from CIAT's Eddie Weir PCIAT.
Rates freeze, NI cuts, full expensing; early election?
Could this be a remedy for condensation, damp or mould?
Unlocking a Healthier Tomorrow
Call for ministerial group and National Retrofit Delivery Plan.
The Great Transformation 1860–1920. Book review.
Including the devolved governments, CIOB, ECA, APM and IHBC.
AT awards small to medium size project category winner.
Formal and informal adaptive re-use or new use of buildings.
Temperatures hit new highs, yet world fails to cut emissions (again).