Foundation movements

The prediction of foundation movement is based on knowledge of how foundation loads are transferred to the ground and how the earth and rock materials respond to stress increases. One of the more destructive movements is caused by differential settlements, and their occurrence can often be attributed to local variations in soil compressibility; variation in thickness of compressible soil; differences in footing sizes and pressures; variations in applied load or differences in embedment depth of footings. Three basic types of settlement are uniform, tilt and non-uniform settlement. The "allowable" settlement depends on the type of structure, its size and intended use. Not all movements are unrelated to foundation pressure. The most important are a result of soil shrinkage and swelling. Shrinking is caused by the removal of water, such as "drying out" due to long periods of draught, or removal of water by tree roots. Swelling results from fresh supplies of water not available when the structure was built. Swelling and shrinkage, however, normally occur in fine-grained soil with a large clay content. Other causes of foundation movement may be the result of soil freezing, causing soil heaving, or in the cause of pyritic shales, oxidization which results in volume increase. It is important to remember that all foundations move; the challenge is to predict the behaviour of the foundation and appreciation for the interaction of the soil and the structure.Aussi disponible en fran\ue7ais : Mouvements de fondationsPeer reviewed: NoNRC publication: Ye