Compensated foundation
Contents |
[edit] Introduction
Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics to support them.
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.
Compensated foundations normally comprise a deep basement and/or are used to support tall buildings or swimming pools, where a very large amount of material is excavated.
In addition to the control or elimination of settlement in the soil, other advantages include:
- 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.
[edit] Compensated raft foundations
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.
[edit] Compensated piled raft foundations
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.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Specifying rendered external wall insulation for fire safety
How to interrogate the evidence provided to the specifier.
The benefits of writing articles for your organisation
How to create a profile for your organisation and publish for free.
No Falls Week. The importance of safe working at height
What to expect and what is on offer to avoid accidents.
Scottish Government action to reach net-zero targets
Retrofit expert group highlight critical actions needed.
A forward thinking, inclusive global community of members.
From engineered product life-spans, to their extension.
Circular economy in the built environment
A brief description from 2021. Where are we now?
Mental Health Awareness Week with ABS
Architects Benevolent Society programme of activity.
CLC publishes domestic retrofit competency framework
Roadmap of Skills for net zero.
May 13-19: Moving more for our mental health.
Understanding is key to conservation.
Open industry engagement survey seeks responses
Institutions and the importance of engagement.
National Retrofit Hub unveils new guide
Digital Building Logbooks and Retrofit: An Introduction.
Enhancing construction site reporting efficiency
Through digitisation and the digital revolution.