The lowest part of a structure that transmits its weight to the underlying soil or rock is the foundation. Foundations can be classified into two major categories-shallow foundations and deep foundations. Individual footings (Figure 1.1), square or rectangular in plan, that support columns and strip footings that support walls and other similar structures are generally referred to as shallow foundations. Mat foundations, also considered shallow foundations, are reinforced concrete slabs of considerable structural rigidity that support a number of columns and wall loads. Several types of mat foundations are currently used. Some of the common types are shown schematically in Figure 1.2 and include

1. Flat plate (Figure 1.2a). The mat is of uniform thickness. 2. Flat plate thickened under columns (Figure 1.2b). 3. Beams and slab (Figure 1.2c). The beams run both ways, and the columns

are located at the intersections of the beams. 4. Flat plates with pedestals (Figure 1.2d). 5. Slabs with basement walls as a part of the mat (Figure 1.2e). The walls act

as stiffeners for the mat.