Raft Foundation
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.
Did you like this article on Raft or Mat foundation? Let us know in the comments.
Dear Sir,
I am not clear how nearness of water table under the raft will impact on its performance. I shall be obliged for necessary elaboration and possible illeffects in future.
You have mentioned “edge erosion may occur if not treated properly”. What treatments are needed in this case to safeguard against it.
I really love this forum because it give hope to this our generation! Raft foundation and inverted slab raft ate for different site soil nature. Can you please explain.
The function of raft foundation needed