Cellular Raft.

A cellular raft consists of an arrangement of two-way interlocking foundation beams with a ground bearing slab at  the underside and a suspended slab at the top surface. The upper and lower slabs are usually incorporated within the beams to form I sections. The intersecting beams effectively break the large slab into two-way spanning continuous small panels (see Fig. 9.26).

The top slab is cast using precast soffits or other forms of permanent formwork such as lightweight infill blocks.

These rafts are used on sites subject to severe mining activity or in areas of poor ground where large bending
moments are to be resisted. They are also used in locations where a valuable increase in bearing capacity can be achieved by the removal of the overburden and where deep foundation beams are required.

Fig. 9.26 Cellular raft.