The impact of extended depth-of-cut mining on coal mine ground control and worker safety

The rapid acceptance of extended (deep) cutting in U.S. underground coal mines has occurred in advance of any significant health-and-safety research efforts to assess the potential ground control hazards and worker safety concerns of employing this mining system. Since 1988, the number of mines approved to extract extended cuts has increased nearly 70 percent. Extended depth-of-cut mining, utilizing remotely controlled continuous mining machines, involves the extraction of coal at cut depths ranging from 20 to 65 ft (6 to 20 m). Because the areal extent of unsupported roof is greater than those resulting from typical ({dollar}le{dollar}20 ft (6 m)) cut depths, roof failures are a concern. The primary extended-cut ground control problem addressed is: Does extended cutting expose mine workers to greater risks of injury from roof falls, both during and after coal extraction. The worker safety concerns addressed included remote-control operation and operator positioning during extended-cut mining.; The ground-control concerns of extended-cut mining were addressed through statistical analyses of reported roof-fall accidents and fatalities, finite element computer modeling to predict strata deformation and stress concentrations, and underground investigations to monitor roof strata deformation and to relate roof stability and cut depth during extended cutting. In addition, the engineering and geologic characteristics associated with extended cutting were collected at a number of mines, to determine the factors critical to safe extended cutting.; The worker safety issues were addressed through extensive in-mine data collection, by observing remote operation of the continuous mining machine at the face, from mine worker interviews, and by analyzing mining and coal extraction methods.; The results indicate that extended-cut mining is a widely accepted practice, and is expected to continue to be used in the U.S. underground coal mines. It can be a safe coal extraction method if mine operators and workers follow the guidelines developed by the regulatory agencies and by taking extra precautions to avoid the unsupported roof and operator positioning problems during the remote-control operation of the continuous mining machine.