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Underground coal mining has occurred beneath eight million acres of land in the United States, two million acres of which have been affected by subsidence. Most of this mining has taken place in the eastern half of the United States (east of the 100th meridian) where thousands of acres in urban areas are threatened by subsidence.

Early mining was not as efficient as today. Unrecovered coal pillars, often of variable size and spacing, remain to support the overlying strata for an indefinite period of time after mining has ceased. Roof collapse, crushing of pillars, or punching of pillars into the floor is now resulting in sinkhole or trough subsidence tens or even hundreds of years after mining.

In areas of active mining, where nominal total extraction is practiced, subsidence is essentially contemporaneous with mining. Limited observational data on ground movements over total extraction mines–room and pillar and longwall–suggest subsidence over deep longwall mines in Europe is similar in general respects, but different in detail, to subsidence in the United States.

Ground deformations resulting from subsidence have often been assumed to cause damage to structures in terms of simple tension and compression transferred by friction and adhesion to the undersides of foundations. Differential settlement, intensified pressure on subgrade walls, and other modes of soil-structure interaction are of equal significance in the eastern United States.

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