#103 Raft Foundation - Its Advantages and Disadvantages

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.
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.

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.

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.

RCC Construction , Pratapnagar