Determination of transition depth between slope and box-cut access for near-surface coal reserves

The depth at which it becomes more economical to use slope access instead of box-cut access for near-surface coal reserves is termed the "transition depth." The transition depth can be established for a given coal property by considering cost estimates for those parameters that determine respective access methods. Fourteen parameters that influence access cost were identified, and ranges for these parameters were determined. A transition-depth formula was developed to permit the determination of which is the better method of accessing a reserve, given information such as highwall slope, road width, total bench width, pit dimensions, road grade, belt component costs, pumping costs and the cost of overburden removal and reclamation. In most cases in Appalachia, especially in eastern Kentucky, the observed transition depth ranges from 20 to 30 m (66 to 100 ft). This indicates that actual practice is consistent with the analytical approach used.