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Subsidence research by the U.S. Bureau of Mines has identified and documented the occurrence of landslides over a longwall mining area in the Dunkard basin. Most of these landslides occurred in masses of slumped hummocky soil generally associated with limestone and claystone beds of the Washington and Greene Formations. Identification and characterization of this phenomenon are needed to model accurately the future effect of subsidence-related surface damage to postmining land use.
Mining by longwall methods has been observed to produce a gradual surface subsidence profile of up to 60% of the thickness of the mined coal bed. The gradual subsidence of panels averaging 600 × 5,000 ft (180 × 1,525 m) can cause reactivation of older landslide deposits by decreasing the support to the landslide toe area. Examination of surficial features over a longwall mining area comprised of nine panels has led to the identification of several reactivated landslides. The two largest landslides occurred above a thin sandstone member with several associated springs. The largest landslides ranged from 100 to 300 ft (30 to 90 m) in length and from 100 to 200 ft (30 to 60 m) in width. Maximum scarp-slope displacements were approximately 7 ft (2 m). Less significant mass wasti g was also observed over the longwall panels. Identification of landslides was accomplished through examination of premining aerial photographs and geologic field investigation. Characterization of reactivated zones was achieved through evaluation of current aerial 2-ft (0.6-m) surface contour map and field surveys. Recognition of problem areas will make civic and mining personnel aware of the landslide potential so that damage in such areas can be minimized.
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