WHILE it is generally known that building frames, like other statically indeterminate structures, are very sensitive to unequal settlement, they are almost invariably designed and erected on the assumption of perfectly rigid foundations or, at the most, it is considered that an equal permissible bearing pressure throughout the site causes a negligible and uniform settlement, over the whole loaded area. Field observations 3 14 and theoretical investigations 9 l6 show that such loads, even where they are based on an adequate factor of safety against failure of the ground, do not limit the settlement of structures to it definite and safe magnitude nor do they ensure its uniform distribution over the foundation area except for very stiff rafts. FPom these records it can be concluded that an average subsidence of 1in. to 2in. can generally
not be avoided and is often harmless; if it exceeds 3in., however, the corresponding relative movement of the supports frequently causes considerable damage to the superstructure, especially where the usual individual footings or flexible rafts are provided.
George Geoffrey Meyerhof