Engineering and Construction

All foundations settle to some extent as the earth materials around and beneath them adjust to the loads of the building. Foundations on bedrock settle a negligible amount. Foundations in other types of soil may settle
much more. As an extreme example, Mexico City’s Palace of Fine Arts has settled more than 15 feet (4.5 m) into the clay soil on which it is founded since it was constructed in the early 1930s. However, building foundation settlement is normally limited to amounts measured in millimeters or fractions of an inch.

Where  foundation settlement occurs at roughly the same rate through-out all portions of a building, it is termed  uniform settlement. Settlement that occurs at differing rates between different portions of a building is termed  differential settlement. When all parts of a building rest on the same kind of soil, and the loads on the building and the design of its structural system are uniform throughout, differential settlement is normally not a concern.

However, where soils, loads, or structural systems differ between parts of a building, different parts of the building structure may settle by substantially different amounts, the frame of the building may become distorted, floors may slope, walls and glass may crack, and doors and windows may not work properly (Figure 2.1). Most foundation failures are attributable to excessive differential settlement. Gross failure of a foundation, in which the soil fails completely to support the building, is extremely rare.

Figure 2.1 Uniform settlement (b) is usually of  little consequence in a building, but differential settlement (c) can cause  severe structural damage.