Face Length Optimization in Mechanized Retreating longwall Method

Abstract

Longwall panels, where geologically possible, are becoming larger everyday. The increase in size is limited by rock mechanics and economic factors . In a caving longwall panel, as the face length increases, pressure exerted on the edges of the entries on both sides of the panel increases up to a limit and then decreases .From this point , only the pressure on the face ends increases , although more slowly. The induced stress lies within the mineral and hence only affects the sides of the adjacent roads and not the immediate roof. The capacity of the powered supports therefore need not increase with the length. The only problem remains to be possibility of rock bursts and the instability at the cross-sections with the face, before yielding of the rock that occurs at the start of coal outing and before caving is completed. Total production costs increase with the face length but not proportionately. Unit costs therefore decrease with increases in face length and after a point they start to rise. The optimum face lengths, where unit production costs are at minimum, are calculated here.