A model for extended bench casting in dipping coal seam

Abstract

This paper deals with extended bench casting with draglines in surface coalmines. A computer model, developed for panel design, covers three fundamental operating modes: i) level casting for flat-lying coal seam; ii) downhill casting; and iii) uphill casting for inclined coal seam conditions. Influence of pit width on critical pit dimensions such as cut length, dragline reach on key cut and main cut positions, swing angles on key cut and main cut positions and rehandle percentage is critically studied. The model is equipped with a device to determine total number of points within a cut on which dragline is placed. With another module, walking pattern of dragline between adjacent cuts is decided. The model indicates that coal seam inclination significantly influences dragline productivity. All things being equal, the uphill operation mode demands larger dragline dimensions. Extended bench construction in uphill casting is easier and faster as less material is required. Besides, dragline operates on a safe bench. As coal seam gets inclined, a large dragline may switch from extended benching in downhill mode to direct casting owing to the room available for spoil piles increases with coal seam inclination. However, a small dragline would likely fail to operate in downhill mode as the size of the extended bench would expand faster than the waste available in the cut. Besides, dragline would not be adversely affected by failures occurring in spoil piles. It has been observed that in extended benching practice with an inclined coal seam downhill casting should be considered first.