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.