Mat Foundation Settlement

Under some conditions spread footings would have to cover more than half the building area and mat foundations might be more economical.

Mat foundation settlement. Common types of mat foundation. The settlement tends to be controlled via the following. It is common to use mat foundation or deep basements to transfer the column loads to the underlying soil as well as provide floor slab for the basement. Mat foundation is specified to bridge over pockets of weak spots in moderately weak soil.

Compared to spread footings the differential settlement in a mat foundation is much more reduced as the mat bridges over the loose pockets and lenses of a soil deposit. The designer can analyse a mat foundation of any size including up to 32 columns placed anywhere on the foundation. Thus an allowable maximum settlement of 50 mm is usually specified for raft foundations. It is used to reduce differential settlement of buildings.

Mat foundation is also known as the raft foundation. If settlements beneath the mat foundation are more than the rigidity of the structure will permit a redistribution of loads takes place that will. Mat foundations are sometimes preferred for soils that have low load bearing capacities but that will have to support high column or wall loads. A mat foundation is used when the subsoil is weak and column loads are so heavy that the conventional spread footings cover more than 50 of the building area.

Whereas for footings only 25 mm is specified for the same allowable differential settlement of 18 mm 3 4 inches for both cases. The settlement of the mat foundation will be within limits that the structure can safely tolerate as a flexible structure. The mat foundation can be analysed as either rigid or flexible depending on the size and thickness of the mat and the strength of the subgrade. It is a continuous thick concrete slab on the soil that extends the entire footprint of the building and increases the soil bearing capacity power.

Use of a larger foundation to produce lower soil contact pressures. Mat foundations are commonly used where settlements may be a problem for example where a site contains erratic deposits or lenses of compressible materials suspended boulders etc. It has been found that for the same loading intensity and soil condition the differential settlement in a mat foundation is about 1 2 than that of a spread foundation. The columns can be subjected to axial horizontal and moment forces.

Mat foundation is also used for low bearing capacity soil in order to spread the load of a building and hence construct a stable foundation. Mat foundations are popular in areas where basements are common.