Mat or raft foundation is a large slab supporting a number of columns and walls under the entire structure or a large part of the structure to lower the contact pressure compared to spread footing.
When Mat/Raft Foundation is Recommended
It is recommended for the following purposes.
- Bearing capacity of soil is low,
- walls of the structure are so close that individual footings would overlap,
- it is used for large loads,
- individual footings would cover more than about half of the construction area.
Advantages of Raft Foundation
It has many advantages as well as disadvantages. The advantages of raft foundation are as follows,
- Raft or mat foundation is economic due to combination of foundation and floor slab.
- It requires little excavation.
- It can cope with mixed or poor ground condition.
- It reduces differential settlement.
Disadvantages of Raft Foundation
It has some disadvantages also. The disadvantages of raft foundation include the following.
- Mat foundation requires specific treatment for point loads.
- Edge erosion occurs if not treated properly.
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