Mat foundation is otherwise called as Raft Foundation and its working principle is similar to shallow foundation. Mat foundation is preferred for large space where separate footings are not possible to construct due to overlapping condition. Generally, Mat foundation’s footing will extend over a large area. The main reason why the Mat adopted by most Engineers is Mat will distribute loads equally to prohibit differential settlement. Mat is considered when the soil condition is so poor & weak.
Mat foundations are selected when:
The area covered by the individual footings exceeds 50% of the structural plan area. This is usually the case for buildings higher than 10-stories.
The building requires a deep basement, below the phreatic surface. For example, to buildseveral levels of parking, for mechanical systems, access to subway stations.
The Engineer wishes to minimize the differential settlement in variable (that is, heterogeneous) soils, or if pockets of extremely weak soils are known to be present.
The Engineer wishes to take full advantage of the soil’s increasing bearing capacity with depth by excavating basements, and thereby seek a fully or a partially compensated foundation.
Types of Mat Foundation:
- Flat plate mat
- Plate thickened under columns
- Two-way beam and slab
- Plate with pedestal
- Rigid frame mat
- Piled raft
