mining conditions, areas of poor ground where the raft will be subjected to large bending moments, etc. The main difference however is the use of a lighter form of upper slab designed to be separate to the main foundation (see Fig. 9.27).
The detail at the seating of the upper ﬂoor depends upon the need for re-levelling and the possible number of times adjustments to line and level may be necessary.
Fig. 9.27 Lidded cellular raft.