slope

…a pit have a certain slope determined by the strength of the rock mass and other factors. The stability of these walls, and even of individual benches and groups of benches, is very important—particularly as the pit gets deeper. Increasing the pit slope angle by only a few degrees can…

…three types of portal: drift, slope, and shaft. Where a coal seam outcrops to the surface, it is common to drive horizontal entries, called drifts, into the coal seam from the outcrop. Where the coal seam does not outcrop but is not far below the surface, it is accessed by…